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  `Migration#change` can reverse is out of date.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.

Closes #21418.

Previously schema names were not quoted. This leads to issues when a
schema names contains a ".". Methods in `schema_statements.rb` should
quote user input.

These changes rephrases the description with better explanation of step by step process.

[Feature] params.require accepts array of parameters that should be present or raise error

This PR adds ability to accept arrays which allows you to require multiple values in one method. so instead of this:

```ruby
params.require(:person).require(:first_name)
params.require(:person).require(:last_name)
```

Here it will be one line for each params, so say if I require 10params, it will be 10lines of repeated code which is not dry. So I have added new method which does this in one line:

```ruby
params.require(:person).require([:first_name, :last_name])
```

Comments welcome

[ci skip]

Currently the `#tables` method does not make use of the `name`
argument and always returns all the tables in the schema search
path. However the docs suggest different behavior.

While we should porbably adjust the implementation to provide this
behavior, let's make the docs right for now (also for `4-2-stable`) and
then implement the behavior on `master`.

fix reference to undefined variable in email testing guide [ci skip]