* 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.

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

This reverts commit cae2b5bb.

I am an idiot.

eventually we'll remove this instance variable, but this is the first
step

we're storing the value in the headers hash, so lets just store the
value in one place.

Modules should be using the API that the abstract modules use so that we
can move these modules between implementations

cookies are always stored as a string in the header hash, so it will not
need to be joined.

eventually we will refactor this to not know about header hashes

Follow up to #21384.

Cleanup for `ActionDispatch::Http::Parameters` - no need for required libraries
and remove not used private method.

Apparently this method was used in `ActionDispatch::Http::Request` - fixed
by calling `Request::Utils` explicitly (as was done in other parts of the codebase)

Rack::Response::Helpers implements this method, so we can safely remove
it

If the response method is defined, then calling `response` will return a
response.

If AV::Rendering is mixed in, then `rendered_format` will be calculated
based on the current `lookup_context`, but calling `_process_format`
will set the `rendered_format` back on to the same lookup context where
we got the information in the first place!

Instead of getting information from an object, then setting the same
information back on to that object, lets just do nothing instead!

Apparently the AbstractController (whatever "abstract" means) is
expected to work without a request and response.

`render` is the only possible source for the `plain` option.  Pulling
the conditional up to the `render` method removes far away conditionals

We don't need to pass the full hash just to pull one value out.  It's
better to just pass the value that the method needs to know about so
that we can abstract it away from "options"

Since all controller instances are required to have a request and
response object, RackDelegation is no longer needed (we always have to
delegate to the response)

the subclass sets the body on the response object, so we don't need the
superclass doing it too

without this module, the content type is not set correctly

Now that `Controller#status=` just delegates to the response object,
we don't need to set the response on the controller and the response.
We can just set it in one place.

we always have a response object, so there is no reason to test it

these ivars don't exist anymore, so we can remove them from the list

since the controller always has a request on it, we can just ask the
request for the content type.

The controller instance always has an instance of a response object.  We
should store the status code on the response object so that it's only
store in one place.

We always have a response object in controller instances, so we can
remove this conditional

controller instances always have a response object, so we don't need to
test to see if there is one, just always call to_a on the response.

The following Rails code failed (with a `KeyError` exception) under
test:

```ruby
class ApplicationController < ActionController::Base
  def user_strategy
    # At this point:
    # ```ruby
    # session == {
    #   "user_strategy"=>"email",
    #   "user_identifying_value"=>"hello@world.com"
    # }
    # ```
    if session.key?(:user_strategy)
      session.fetch(:user_strategy)
    end
  end
end
```

When I checked the session's keys (`session.keys`), I got an array of
strings. If I accessed `session[:user_strategy]` I got the expected
`'email'` value. However if I used `session.fetch(:user_strategy)` I
got a `KeyError` exception.

This appears to be a Rails 4.2.4 regression (as the code works under
Rails 4.2.3).

Closes #21383

Controllers should always have a request and response when responding.
Since we make this The Rule(tm), then controllers don't need to be
somewhere in limbo between "asking a response object for a rack
response" or "I, myself contain a rack response".  This duality leads to
conditionals spread through the codebase that we can delete:

  * https://github.com/rails/rails/blob/85a78d9358aa728298cd020cdc842b55c16f9549/actionpack/lib/action_controller/metal.rb#L221-L223

collect the body and make assert against the collected body

we don't need an instance to figure out what type of response to
allocate.  Later we'll pull this up the stack and pass the response
object down

This saves a lambda and request allocation on each request.

controllers should always go through the `action` class method so that
their middleware is respected.

now the caller can just treat it like a regular controller even though
it will return a 404