Fixes #16255 [ci skip]

* Allow to specify a type for foreign key column in migrations
* unified the docs
* some cleanup in CHANGELOG

[Andrey Novikov & Łukasz Sarnacki]

Make sure assertion passes for postgresql.

Remove redundant reset that already happened in teardown.

The fixtures are still in play, adding a new column without a default and `null: true`
is not possible. This reverts back to leaking global state, as our `schema.rb` adds
the `null: false` constraint on this field.

A future solution would be to make the `migration_test.rb` run independent of fixture tables.
This way we can simply drop the state after test execution, without worrying about side effects.

/cc @zuhao

Remove length limit that results failure in other tests.

[ci skip]

Remove the side-effects of validates_presence_of.

Added some missing activesupport test coverage

Remove not-required file class/subclasses

Touch option description grammatical error fixed [ci skip]

Generators guide grammatical error fixed [ci skip]

[ci skip] Fix code in Routing Guide

Conflicts:
	actionpack/test/abstract_unit.rb

We are planning to remove mocha from our test suite because of
performance problems. To make this possible we should stop require mocha
on ActionSupport::TestCase.

This should not affect applications since users still need to add mocha
to Gemfile and this already load mocha.

Added FIXME notes to place that still need mocha removal

Missing test for form values before type cast

Some ActionView renderer refactors

Fixed typo in comment [ci skip]

Make create_join_table use the same logic as HABTM reflections

Fixes to request method test.

Additional help messaging to help the user resolve a conflicted migration

Cleanup + CHANGELOG for pr #14886

Also cleanup test a bit

[related #14886]
[related #14743]

The entire 127.0.0.0/8 range is assigned to the loopback address, not
only 127.0.0.0/24. This patch allows ActionDispatch::Request::LOCALHOST
to match any IPv4 127.0.0.0/8 loopback address.

The only place that the #local? method was previously under test was
in the show_expectations_test.rb file. I don't particularly like that
that's implicitly where this code is under test, and I feel like I
should move some of that testing code into the
test/dispatch/request_test.rb file, but I wanted some feedback first.

Credit goes to @sriedel for discovering the issue and adding the
patch.