* Summary: fix slowness due to layout thrashing when reloading a large set of status updates

in order to limit the maximum size of a status in a list view (e.g. the home timeline), so as to avoid having to scroll all the way through an abnormally large status update (see https://github.com/tootsuite/mastodon/pull/8205), the following steps are taken:
•the element containing the status is rendered in the browser
•its height is calculated, to determine if it exceeds the maximum height threshold.
Unfortunately for performance, these steps are carried out in the componentDidMount(/Update) method, which also performs style modifications on the element.  The combination of  height request and style modification during javascript evaluation in the browser leads to layout-thrashing, where the elements are repeatedly re-laid-out (see https://developers.google.com/web/fundamentals/performance/rendering/avoid-large-complex-layouts-and-layout-thrashing & https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Performance_best_practices_for_Firefox_fe_engineers).
The solution implemented here is to memoize the collapsed state in Redux the first time the status is seen (e.g. when fetched as part of a small batch, to populate the home timeline) , so that on subsequent re-renders, the value can be queried, rather than recalculated.  This strategy is derived from https://github.com/tootsuite/mastodon/pull/4439 & https://github.com/tootsuite/mastodon/pull/4909, and should resolve https://github.com/tootsuite/mastodon/issues/12455.

Andrew Lin (https://github.com/onethreeseven) is thanked for his assistance in root cause analysis and solution brainstorming

* remove getSnapshotBeforeUpdate from status

* remove componentWillUnmount from status

* persist last-intersected status update and restore when ScrollableList is restored

e.g. when navigating from home-timeline to a status conversational  thread and <Back again

* cache currently-viewing status id to avoid calling redux with identical value

* refactor collapse toggle to pass explicit boolean

Fixes #12690

The `strong_migrations` update from ba2eac8824
introduced a check for `change_column_null` specific to Postgres. This rejects
old migrations.

This commit just wraps old migrations with `safety_assured` to bypass this
check. Alternatives would have been to:
- Disable that check entirely (a possibility added in that same
  `strong_migrations` version) for Mastodon, but it makes sense to write new
  migrations without such a strong lock.
- Rewrite the old migrations to do it in a way that do not require an exclusive
  lock. I thought fixing those old migrations for performance wasn't worth the
  pain. Also, if I understand correctly, the next version of
  `strong_migrations` is going to include a helper to do that. We could update
  those migrations at that point.

Bumps [handlebars](https://github.com/wycats/handlebars.js) from 4.2.0 to 4.5.3. **This update includes a security fix.**
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Bumps [@babel/runtime](https://github.com/babel/babel/tree/HEAD/packages/babel-runtime) from 7.7.6 to 7.7.7.
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Bumps [enzyme](https://github.com/airbnb/enzyme/tree/HEAD/packages/enzyme) from 3.10.0 to 3.11.0.
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Bumps [object.values](https://github.com/es-shims/Object.values) from 1.1.0 to 1.1.1.
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Bumps [css-loader](https://github.com/webpack-contrib/css-loader) from 3.3.2 to 3.4.0.
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Bumps [sass](https://github.com/sass/dart-sass) from 1.23.3 to 1.24.0.
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Bumps [rubocop](https://github.com/rubocop-hq/rubocop) from 0.77.0 to 0.78.0.
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Bumps [array-includes](https://github.com/es-shims/array-includes) from 3.1.0 to 3.1.1.
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Bumps [faker](https://github.com/faker-ruby/faker) from 2.8.1 to 2.9.0.
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Bumps [strong_migrations](https://github.com/ankane/strong_migrations) from 0.5.0 to 0.5.1.
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Bumps [rails](https://github.com/rails/rails) from 5.2.4 to 5.2.4.1.
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Bumps [rack-attack](https://github.com/kickstarter/rack-attack) from 6.2.1 to 6.2.2.
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Bumps [oj](https://github.com/ohler55/oj) from 3.9.2 to 3.10.0.
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One hook was actually duplicated incorrectly; this has been fixed. Another hook was re-ordered for better results in actual use.

Currently the page re-uses strings from other contexts which doesn't fit
very well - strings incorrectly lowercase-d and pluralized, when they
don't need to be, because it's a table.

This commit changes page to re-use accounts.posts_tab_heading for toots,
and admin.accounts for "Following" and "Follows". This all should look
more aesthetically pleasing.

Fixes #12607

`will-change: transform` apparently makes manual scrolling impossible on
Firefox/Windows. While this should probably be considered a Firefox bug,
`will-change: transform` seem like a very aggressive performance hint that
may possibly make the browser consume more resources than needed, especially
in multiple-column mode.

This was originally added to improve scrolling performances on mobile, but
I think this isn't necessary anymore, because of the two following reasons:
- `contain: paint` (which is implied by `contain: strict`, which we apply
  whenever the browser supports grids) should have similar effects
- in single-column mode, the scrolling container is the root element, which
  I believe is optimized in at least Chromium

Keep in mind that I have not been able to make in-depth benchmarks, and
especially not been able to try on mobile, so performances should probably
be investigated further…

Bumps [rack](https://github.com/rack/rack) from 2.0.7 to 2.0.8. **This update includes a security fix.**
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- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rack/rack/compare/2.0.7...2.0.8)

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Instead, just re-use the existing category if any.

Fixes #12608

* Remove unused “salmon_url” string

* Remove more unused translatable strings

The following strings all used to be on the admin account page
but aren't used anymore: profile_url, outbox_url, followers_url, feed_url

The link crawler expects HTML documents, so set the `Accept`
header accordingly.

Fixes #12618

* Bump rails from 5.2.3 to 5.2.4

Bumps [rails](https://github.com/rails/rails) from 5.2.3 to 5.2.4.
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* sprockets ~> 3.7

Bumps [json-ld-preloaded](https://github.com/ruby-rdf/json-ld-preloaded) from 3.0.4 to 3.0.6.
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Bumps [react-redux](https://github.com/reduxjs/react-redux) from 7.1.1 to 7.1.3.
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Bumps [webpacker](https://github.com/rails/webpacker) from 4.2.0 to 4.2.2.
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Bumps [eslint-plugin-import](https://github.com/benmosher/eslint-plugin-import) from 2.19.0 to 2.19.1.
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Bumps [copy-webpack-plugin](https://github.com/webpack-contrib/copy-webpack-plugin) from 5.0.5 to 5.1.1.
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Bumps [css-loader](https://github.com/webpack-contrib/css-loader) from 3.2.0 to 3.3.2.
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Bumps [array-includes](https://github.com/es-shims/array-includes) from 3.0.3 to 3.1.0.
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Bumps [doorkeeper](https://github.com/doorkeeper-gem/doorkeeper) from 5.2.2 to 5.2.3.
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Bumps [stackprof](https://github.com/tmm1/stackprof) from 0.2.13 to 0.2.14.
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Bumps [parallel_tests](https://github.com/grosser/parallel_tests) from 2.29.2 to 2.30.0.
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* Fix comments in statuses_cli

The comment for the part of query keeping statuses which have replies was
incorrect, explaining the part of the query kept favourited statuses instead

* Keep statuses favourited by local users in tootctl statuses remove

* Do delete old replies that are not direct interactions with local users

* Skip reblogs of local statuses instead of all reblogs

* Optimize some queries

* Keep old statuses with recent reblogs

* Add option to clear toots from followed accounts too

* Remove “protocol” argument and return value, as only ActivityPub is supported

* Remove FetchRemoteAccountService, only use ActivityPub::FetchRemoteAccountService

* Fix tests

* Revert "Fix ignoring whole status because of one invalid hashtag (#11621)"

This reverts commit dff46b260b.

* Fix statuses being rejected because of invalid hashtag names

* Add spec for invalid hashtag names in statuses

* Add test for featured tags controller

* Increased max backup size

* partially reverted schema.rb

Bumps [@babel/preset-env](https://github.com/babel/babel) from 7.7.4 to 7.7.6.
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Bumps [compression-webpack-plugin](https://github.com/webpack-contrib/compression-webpack-plugin) from 3.0.0 to 3.0.1.
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Bumps [faker](https://github.com/faker-ruby/faker) from 2.8.0 to 2.8.1.
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