Add test case for clear mappings
Deprecate all *_filter callbacks in favor of *_action callbacks

This is the continuation of the work started at
9d62e04838f01f5589fa50b0baa480d60c815e2c
Merge pull request #15373 from akshay-vishnoi/test-cases

Add test case for clear mappings
Merge pull request #15269 from arunagw/aa-fixes-8930

rake railties:install:migrations respects the order of railties
Add CHANGELOG entry for #15269 [ci skip]
Remove AR Properties from the public API

Making this part of the public API was premature, let's make it private
again while I continue to work on the surrounding code.
Merge pull request #15374 from sgrif/sg-private-properties

Remove AR Properties from the public API
Move types to the top level `ActiveRecord` namespace

`ActiveRecord::ConnectionAdapters::Type::Value` =>
`ActiveRecord::Type::Value`
pg, keep `hstore` and `json` attributes as `Hash` in @attributes.

The solution presented in this patch is not efficient. We should replace it
in the near future. The following needs to be worked out:
  * Is `@attributes` storing the Ruby or SQL representation?
  * `cacheable_column?` is broken but `hstore` and `json` rely on that behavior

Refs #15369.

/cc @sgrif @rafaelfranca
Initial doc for TransactionIsolationError [ci skip]
Add with_default_charset helper.
Merge pull request #15381 from zuhao/refactor_actionpack_content_type_test

Add with_default_charset helper.
Move I18n.locale setting into setup and teardown.
Merge pull request #15383 from zuhao/refactor_actionpack_localized_templates_test

Move I18n.locale setting into setup and teardown.
Add and remove renderer inside the test to prevent leak.
Avoid hardcoded value in teardown.
Merge pull request #15385 from zuhao/refactor_actionpack_render_other_test

Add and remove renderer inside the test to prevent leak.
Remove unused `Column#coder`

It appears this property was added, but never actually used. It would be
broken if it were, as it only type casts one way.
Unregister Mime::Type in teardown.
Merge pull request #15388 from zuhao/refactor_actionpack_send_file_test

Unregister Mime::Type in teardown.