missing activesupport test coverage
Fix AC::TemplateAssertions instance variables not resetting.

Fixes https://github.com/rails/rails/issues/16119.
Remove not-required file class/subclasses
Generator guide grammatical error fixed [ci skip]
Merge pull request #16240 from siddharthbhagwan/master

Generators guide grammatical error fixed [ci skip]
Touch option description grammatical error fixed [ci skip]
Merge pull request #16242 from vadivelan-k/content_verifier

Touch option description grammatical error fixed [ci skip]
Merge pull request #16239 from akshay-vishnoi/remove-require

Remove not-required file class/subclasses
Merge pull request #16232 from egilburg/activesupport_coverage

Added some missing activesupport test coverage
Remove the side-effects of validates_presence_of.
Merge pull request #16248 from zuhao/refactor_activerecord_presence_validation_test

Remove the side-effects of validates_presence_of.
docs, add example for running a single test against core adapters.

[ci skip]
Remove length limit that results failure in other tests.
Merge pull request #16250 from zuhao/refactor_activerecord_migration_test

Remove length limit that results failure in other tests.
build fix, remove not null constraint.

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
Make sure assertion passes for postgresql.
Remove redundant that already happened in teardown.
Merge pull request #16254 from zuhao/refactor_activerecord_attribute_decorators_test

Remove redundant reset that already happened in teardown.
Merge pull request #16253 from zuhao/refactor_activerecord_nested_through_associations_test

Make sure assertion passes for postgresql.
Allow to specify a type for foreign key column in migrations

[Andrey Novikov & Łukasz Sarnacki]