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

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

They are already required in `actionpack/lib/action_dispatch.rb` (L25-L26)

This `protected` keyword looks like some leftover, since
we are not using explicit receiver, this should go under `private`

We don't want to directly access the env hash

I want to implement this with something besides `@env` in the future, so
lets stop directly referencing it.

superclass already has this method, so remove this one

the dispatcher class isn't configurable anymore, so pull up allocation
to the method that needs it.

Now that we don't have subclasses depending on this method (they augment
the request class instead of the dispatch class) we can remove this
method and directly ask the request object for the controller class

we don't need it anymore.  We always use the same dispatcher in tests.

controller class resolution has been moved to the request object, so we
should override that method instead of relying on the RouteSet to
generate the controller class.

we already have a request, so we should use the methods on the request
to access the path info information

Creates fewer request objects and helps to abstract away from internals

try to remove dependencies on `@env` so we can have more flexible
internals

May be missed in 5fe14163 commit
Also fixes the broken build

This commit allows us to use one request object rather than allocating
multiple request objects to deal with the session.

We're going to implement storing env values differently in the future,
so let's disconnect these methods from the instance variables

we're already doing this with a bunch of other header data.

we have a method that knows how to get rack.input, so lets use that.

We need to abstract the internals of the request object away from this
instance variable so that the values for `@env` can be calculated in a
different way.

Since none of the action pack tests failed without this conditional it
didn't seem necessary. This fixes the build because it correctly returns
a 404 instead of a 500 for the asset routes test.

Test that was failing was in the `assets_test.rb` file and was the test
named `test_assets_routes_are_not_drawn_when_compilation_is_disabled`.