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

Support for custom regular expression for number_to_delimeted

- Extracted `DELIMITED_REGEX` to `delimited_regex` method and made use of  user passed `options[:delimited_regex]` if available. Changed `DELIMITED_REGEX` to `DEFAULT)DELIMITED_REGEX` to signify what it means.
- Added tests for number to delimited and number to currency in both actionview and activesupport.

Changes

Changes

Code cleanup

10X speed improvements for AS::Dependencies.loadable_constants_for_path

Fix Configuring Active Record  [ci skip]

When the autoload_paths start to grows, this methods is quite a hotspot

>> ActiveSupport::Dependencies.autoload_paths.size
=> 49

>> Benchmark.ips { |x| x.report('baseline') { ActiveSupport::Dependencies.loadable_constants_for_path(File.expand_path('app/models/shop')) }}
Calculating -------------------------------------
            baseline    90.000  i/100ms
-------------------------------------------------
            baseline      1.073k (±20.2%) i/s -      4.950k

After the patch

Calculating -------------------------------------
             patched   883.000  i/100ms
-------------------------------------------------
             patched     11.050k (±19.7%) i/s -     50.331k

remove link to outdated article in plugins guide [ci skip]

linked article is a description of the plugins in Rails 2.1.

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.

Merge pull request #21384 from jeremyf/updating-ActionController-TestSession-to-behave-as-a-hash-with-indifferent

Updating TestSession to access with indifference

remove require of files under support that do not use

no more require minitest mock here

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.

I do not know why files under the support has been require.
However, under the support even rails application does not use.
In addition, since the default under the support file nor is generated, it requires I think not necessary

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

Removed duplicate require 'minitest/mock'

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.