Add missing test for #17351

Fix minor typo in README file

With changes made in 8363b8 and ae291421 cookies that are mutated on the
request like `cookies.signed = x` were not retained in subsequent tests,
breaking cookie authentiation in controller tests.

The test added demonstrates the issue.

The reason we need to select from non-deleted cookies is because without
checking the `@delete_cookies` the `cookie_jar` `@cookies` will send the
wrong cookies to be updated. The code must check for `@deleted_cookies`
before sending an `#update` with the requests cookie_jar cookies.
This follows how the cookie_jar cookies from the request were updated
before these changes.

It was not expecting the new `case_insensitive` option to be passed to
`generate_message`, instead of fixing the test we can just not pass this
option down since it is specific to the confirmation validator and not
necessary for the error message.

Fix syntax error introduced by #17351.

Add case_sensitive option for confirmation validation

cache helper with relation not working as expected

Case :- 1. In case of email confirmation one needs case insensitive comparison
        2. In case of password confirmation one needs case sensitive comparison

[ci skip] Update Guides for case_sensitive option in confirmation validation

Fix broken IPv6 addresses handling

Remove dead code

Support MySQL 5.7.8 which enables show_compatibility_56=off

ArrayInquirer to correctly find symbols or strings

We are only supporting Ruby 2.2 and later in Rails 5, so we do not need
an actual constant here. Additionally, referencing a constant actually
does a hash lookup (because constants are not constant in Ruby >_>).
This will be marginally (likely immeasurable) faster. It is less ugly.

Silence callback deprecation warning if testing AJ

Currently the log returned by running ActiveJob tests is filled with:

> DEPRECATION WARNING: Returning `false` in a callback will not implicitly halt a callback chain in the next release of Rails. To explicitly halt a callback chain, please use `throw :abort` instead.

For instance, see https://travis-ci.org/rails/rails/builds/77978273

This happens because some setup and teardown methods [like these one](https://github.com/rails/rails/blob/master/activejob/test/cases/async_job_test.rb#L10-L17)
invoke other methods like `perform_asynchronously!` that can return `false`, but
not with the intention of halting the process if they do.

In my opinion, these deprecation warnings can be silenced to have
the log result cleaner (especially when browsing for errors).

[ci skip] Update what methods `Migration#change` can reverse

* Documentations and comments about what methods
  `Migration#change` can reverse is out of date.
  For example `change_column_default` is now reversible
  by this [commit](https://github.com/rails/rails/pull/20018).

* Comments about `CommandRecorder` dose not match with Rails Guide.
  For example `add_foreign_key` is listed only on Rails Guide.

fix typo in method name [ci skip]

Make revert of `disable_extension` to work

This is fix of #11826 which miss to add `disable_extension` to
`ReversibleAndIrreversibleMethods`. So `CommandRecorder#method_missing`
catches `change_column_default` and @delegate's method is called.

References #19565.

make `ENV` a required argument

Set the content-type to `text/html` if the options[:html] is true

The problem existed where if your ArrayInquirer values were
strings but you checked them using any? with a symbol, it would
not find the value. Now it will correctly check whether both
the String form or the Symbol form are included in the Array.

`

In this commit, we set the content-type to `text/html` in AbstractController if the `options[:html]` is true so that we don't include ActionView::Rendering into ActionController::Metal to set it properly.

I removed the if `options[:plain]` statement because `AbstractController#rendered_format` returns `Mime::TEXT` by default.

* A string in the example lacked quotes.

* The tests asserted stuff about :last_name, whereas
  test params do not have that key.

* But, the first one passed, why? After hitting my head against
  the wall and doing some obscure rituals realized the new
  #require had an important typo, wanted to iterate over the
  array argument (key), but it ran over its own hash keys
  (method #keys).

* Modified the test to prevent the same typo to happen again.

* The second test assigned to an unused variable safe_params
  that has been therefore removed.

* Grammar of the second test description.

* Since I was on it, reworded both test descriptions.