Port compatibility changes from 8f5fdab5bf to glitch-soc

Port 2ee779dcd3 to glitch-soc

Port relevant parts of 9d4541c612 to glitch-soc

Port bb5558de62 to glitch-soc

e.g., typing “blob_cat_p” used to search for “blob” and “cat”, but not
“blob_cat_p”, which means “blob_cat_patpat” is very unlikely to show up,
although it is likely what the user wanted to type in the first place.

Fixes #778

Port f7a6f9489d to glitch-soc

[API] [vanilla required] [glitch-soc optional] initial_state show_sensitive_media boolean changed to show_media string with options "default", "hide_all", "show_all"

Port a060beee72 to glitch-soc

Fixes #678

Port 7901f9f63e to glitch-soc

Port 460e380d38 to glitch-soc

Inspired by f9b23a5d62

Port Mastodon's hashtag stats thing to glitch-soc.
This doesn't change how hashtags are ordered, and doesn't add a trending
hashtags section, but it does change how hashtag searches are rendered,
displaying a trend line alongside each hashtag.

Upstream's implementation has been merged a while ago and is the preferred
way to set fields, as it is the only one compatible with upstream and is
more user-friendly.

This commit deletes the legacy glitch-soc FrontMatter functionality in order
to clean up the code and make it easier to maintain.

Port WebUI part of 0fb0037ca7 to glitch-soc

Port c75493755f to glitch-soc

Fixes #541.

See also the following commits:

- 0c3ce41031
- 268d90e810

So far, glitch-soc used history.length to decide whether to call `goBack()` or
go to / in order to not leave the webUI. This made clicking the “Back” button
go to the “Getting started” column instead of going back in the browser's
history when such an action would leave the web UI, but also when:
- The WebUI is refreshed (F5)
- A tab is restored
- The history length reaches its maximum (e.g., 50 in Firefox)

This commit fixes these shortcomings by checking `window.history.state`.
Indeed, we only want to go back in the browser's history when the current
location has been reached from within the WebUI, which only happens via
`pushState` as far as I know. Since browser store the serialized state in
the browser history, this also survives page reload and session restoration.

Port dafd7afc5e to glitch-soc

Port 0ba49eca8b to glitch-soc

Port 9a1a55ce52 to glitch-soc

Port 0128b86d30 to glitch-soc

Port d185f3ddaf to glitch-soc

This doesn't change anything for glitch-style fields, but those will go
away eventually

Port the UI part of 76f3d5d16b to glitch-soc

Unlike boosts and like, there is no confirmation dialog as misclicking
can be recovered without another user seeing it.

Port 5131012505 to glitch

flavours/glitch/util/initial_state is used in places where we want to
exhibit different behavior based on user preferences.  This means that
it's used in places where no preference is defined, i.e. on an
unauthenticated access.  All values exported from that module must
therefore expect that case; previously, the max chars value didn't.

Addresses #306.

max_toot_chars is present in the root of the initial state object.
(Previously, we were trying to read it from the meta child object.)