in the 4.2 Release Notes [skip ci]

Change to link suggested by @zzak [skip ci]

The error was moved outside of the `ClassMethods` module.

*   Leave two blank lines between sections/packages for readibility.

*   Always indent bullet points with four spaces. This allows multi-paragraph
    points to align properly (see #16103), and it is the same as the format we
    already use in CHANGELOGs. Doing this consistently sets an easy precedent
    for future contributors to follow.

*   Always put the PR/commit link on its own line in the source. If the bullet
    point spans multiple paragraphs, put it on its own paragraph at the end.

[Godfrey Chan & Juanito Fatas]

Also reordered some of the items to put newer ones on top (same order as
CHANGELOGs), which makes it easier to diff while we are still working on it.

This way when we do next release notes, this would be easier to copy and change.

Reliant on https://github.com/rails/rails/pull/15747 but pulled to a
separate PR to reduce noise. `has_many :through` associations have the
undocumented behavior of automatically detecting counter caches.
However, the way in which it does so is inconsistent with counter caches
everywhere else, and doesn't actually work consistently.

As with normal `has_many` associations, the user should specify the
counter cache on the `belongs_to`, if they'd like it updated.

Noticed that there was no section about Action View and added the heading.
Notable changes need to be compiled.

/cc @chancancode @zzak

[ci skip]

/cc @chancancode @zzak

Point to future 4-2-stable branch for detailed changes. [ci skip]

Sync Active Support changelogs with release notes [ci skip]

4.2 Release Notes is a work in progress [ci skip]

Assorted fixes for AS release notes [ci skip]

* `Hash#deep_transform_keys` has already been backported
* Mentioning `ActiveSupport::SafeBuffer#prepend` in the "Deprecations" section would be enough
* Fix syntax in `Kernel#concern` example

Sync AS release notes with the latest commits [ci skip]

Synced 4.2 release notes with commits in railties [ci skip]

Sync AP Deprecations and Notable changes from CHANGELOG [ci skip]

Removed 4.2 release notes from the index [ci skip]

This deprecation was reverted in 489a8f2a [ci skip]

Synced Active Record changelogs for 4.2 release notes [ci skip]

Synced Active Model changelog with the release notes [ci skip]

Added cc26b6b7 as a 'Removal' item in AP release notes [ci skip]

Use 'character' instead of 'symbol' to avoid confusion [ci skip]

Edit pass on 4.2 release notes [ci skip]

📝 💄 Use `.xyz` and `#xyz` appropiately [ci skip]