Add link to API documentation [ci skip] 

Fix typo in the security guide

[ci skip]

Add missing documentation for MemoryStore#clear [ci skip]

Use correct value in `reverse_merge` test

[docs] remove unnecessary sentence

[ci skip]

Added `reverse_merge`/`reverse_merge!` to AC::Parameters:

[Rafael Mendonça França + Mitsutaka Mimura]

Make sure local cache cleared even it's throwing:

Remove conditions parameter from `NullRelation#delete_all`

Improve readability of testing guide [ci skip]

Small change to improve the readability in section 2.3 of the testing
guide.

We (GitLab) hit into an issue that somewhere in the middleware
chain was throwing `:warden`, which was caught in the wrapping
middleware, but `LocalCache::Middleware` was not aware of it.
It should look like:

``` ruby
result = catch(:warden) do
  @app.call(env)
end
```

Source: https://github.com/hassox/warden/blob/090ed153dbd2f5bf4a1ca672b3018877e21223a4/lib/warden/manager.rb#L35-L37

Using `ensure` could make sure that we would always do the cleanup,
and better yet, avoid `rescue Exception` which we all should know
that could cause some issues which could be very hard to debug.

Please check the discussion thread for more context:
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1402#note_25128108

Follow up of e7381d28.

Show correct commands in help

Mostly just that it's there.

Closes #28193.

Deprecate `Migrator.schema_migrations_table_name`

- This PR adds the `reverse_merge` and `reverse_merge!` method to `ActionController::Parameters`
- Fixes #28353

Fix select with block doesn't return newly built records in has_many association

Previously the system test subclasses would call `driven_by` when the
app booted and not again when the test was initialized which resulted in
the driver from whichever class was called last to be used in tests.

In rails/rails#28144 the `driven_by` method was changed to run `use` on
setup and `reset` on teardown. While this was a viable fix this really
pointed to the problem that system test `driven_by` was a global
setting, rather than a per-class setting.

To alieviate this problem calling the driver should be done on an
instance level, rather than on the global level. I added an `initialize`
method to `SystemTestCase` which will call `use` on the superclass
driver. Running the server has been moved to `start_application` so that
it only needs to be called once on boot and no options from `driven_by`
were being passed to it.

This required a largish rewrite of the tests. Each test needs to utilize
the subclass so that it can properly test the drivers.
`ActionDispatch::SystemTestCase` shouldn't be called directly anymore.

Since using a browser is only for selenium it doesn't really make sense
to have a separate class for handling it there. This brings a lot of the
if/else out of the main SystemTestCase class and into the Driver class
so we can abstract away all that extra work.

See the rationale in the comment found in the patch.

The `select` in `QueryMethods` is also an enumerable method.
Enumerable methods with block should delegate to `records` on
`CollectionProxy`, not `scope`.

Fixes #28348.

Document using `default_url_options` in an ActionMailer class.

Since 67fba0cf `SchemaMigration` model was extracted.
Use `SchemaMigration.table_name` instead.

Tests for delegated public methods on AC::Parameters

Use appropriate type in generators test

This fixes the following thor's warning.

```
Expected string default value for '--generate'; got false (boolean)
```

[ci skip]

Document delegated public methods on AC::Parameters

[ci skip]