Support extended grapheme clusters and UAX 29

Fixes #22773

Fix typo in Testing guide: test -> text

Two USAGE files were referring to Active Record and Active Model
without a space, which is incorrect because we're referring to
the framework name and not the constants.

It didn't mention Action Cable's engine.

Avoid `Time.parse` for static date

It was removed by mistake at 877a411d

  Benchmark.ips do |x|
    x.report('Time.parse') { Time.parse('2011-01-01') }
    x.report('Time.new')   { Time.new(2011, 1, 1) }
  end

  Calculating -------------------------------------
            Time.parse     6.640k i/100ms
              Time.new    15.082k i/100ms
  -------------------------------------------------
            Time.parse     71.915k (± 3.1%) i/s -    365.200k
              Time.new    167.645k (± 3.3%) i/s -    844.592k

Make `postgresql_version` public

Fix test for AC::Parameters#to_unsafe_h

- Test should call `to_unsafe_h` instead of `to_h`

Add `columns_for_distinct` for MySQL 5.7 with ONLY_FULL_GROUP_BY

Fix `test_find_with_order_on_included_associations_with_construct_finder_sql_for_association_limiting_and_is_distinct` to NULL-agnostic way

This is useful to libraries that want to feature gate based on the
version of PostgreSQL the user is connected to. For instance, I want to
know if the user is connected to a version of Postgres that supports
concurrent materialized view refreshes. I could add that as a method on
the adapter as a PR, but rails has no need for this itself.

Rails is already using the postgresql_version for its own feature gating
and this makes that possible for other libraries.

TestController#parameters returns AC::Parameters

Fix documentation for configuring default_charset [ci skip]

Fix typo

[ci skip] Put all removals in its section

Remove not used test fixture

'actionmailer/test/mailers/async_mailer.rb' was deleted by
f9da785d .
This template is not used now.

- Fixes #22836.

Improve `select_one` in `Mysql2Adapter`

Correctly cache create_table_info

Fixes #22827
ActionView::TestCase::TestController#parameters should return an
instance of ActionController::Parameters rather than a hash. This
enables helper methods to use the correct interface.

Add AC::Parameters#include?

Mime negotiation format from extension improvements

Closes #22747

Fixes #22818

Fix - `to_s(:db)` in numeric range

Add test coverage for ActiveSupport::NumericWithFormat#to_formatted_s

Add a missing require to ActiveSupport::NumericWithFormat

Fix #first(limit) to take advantage of #loaded? records if available