* Make Array-creation behavior of Paginable more predictable

Paginable.paginate_by_id usually returns ActiveRecord::Relation, but it
returns an Array if min_id option is present. The behavior caused problems
fixed with the following commits:
- 552e886b64
- b63ede5005
- 64ef37b89d

To prevent from recurring similar problems, this commit introduces two
changes:
- The scope now always returns an Array whether min_id option is present
  or not.
- The scope is renamed to to_a_paginated_by_id to clarify it returns an
  Array.

* Transform Paginable.to_a_paginated_by_id from a scope to a class method

https://api.rubyonrails.org/classes/ActiveRecord/Scoping/Named/ClassMethods.html#method-i-scope
> The method is intended to return an ActiveRecord::Relation object, which
> is composable with other scopes.

Paginable.to_a_paginated_by_id returns an Array and is not appropriate
as a scope.

* Replace incorrect use of distinct with group

Some uses of ActiveRecord::QueryMethods#distinct pass field names but they
are incorrect for the current version of Rails.

ActiveRecord::QueryMethods#group provides the expected behavior and
benefits performance. See commit 6da24aad4c.

* Introduce ApplicationController#cache_collection_paginated_by_id

ApplicationController#cache_collection_paginated_by_id fuses
ApplicationController#cache_collection and Paginable.paginate_by_id.

An advantage of this method is that it prevents from modifying scope which
Paginable.paginate_by_id may provide.
ApplicationController#cache_collection always return an array and there
is no possibility of the scope modification. It is also clear for a
programmer, considering the implication of "cache".

This method can also emit more efficient queries by using
Cacheable.cache_ids before calling Paginable.paginate_by_id.