Fix typos related to ActionDispatch::Http::FilterParameters

Introduce ActionDispatch::DebugExceptions interceptors

2.6 warning: ambiguous first argument

Plugins interacting with the exceptions caught and displayed by
ActionDispatch::DebugExceptions currently have to monkey patch it to get
the much needed exception for their calculation.

With DebugExceptions.register_interceptor, plugin authors can hook into
DebugExceptions and process the exception, before being rendered. They
can store it into the request and process it on the way back of the
middleware chain execution or act on it straight in the interceptor.

The interceptors can be play blocks, procs, lambdas or any object that
responds to `#call`.

Fixes two documentation typos found at ActionDispatch::Http::FilterParameters

Fix name of the test added by #32613

As of now,  `HTMLElement.nonce` seems to work only in Chrome.
So, it should not be used now.
https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/nonce#Browser_compatibility

Fixes #32577.

guides/testing: Pluralize controller and helper class names.

Return back "/" to the end of RAILS_GEM_ROOT

Rails-ujs: Info about stoppable events

This reverts commit 78ff47f3, reversing
changes made to daffe033.

That changelog entry should only be on 5-2-stable

Create a .ruby-version compatible with MRI/JRuby by default

The extracted method is used for `CollectionCacheAssociationLoading`,
still not public API.

[ci skip]

Suppress `warning: ambiguous first argument`

Add missing changelog entry

[ci skip]

https://github.com/rails/rails/pull/32593 was backported to
`5-2-stable` but since 5.2.0 is released the changelog entry should
be in Rails 6.0.0 too.

[ci skip]

- The "/" was removed in 40bdbce1 during
refactoring. It may cause regression since looks like was added
intentionaly because it is possible that a name of any another gem
can start with /rails/, so slash was added to ensure that it is "rails"
gem.
I would like to backport this to `5-2-stable` too.

- Use `__dir__` instead of `__FILE__`. Follow up #29176.

Fix relation merging with skip_query_cache!

Allow rubocop check more files

This commit fix pattern of filenames for `CustomCops/AssertNot` and
`CustomCops/RefuteNot`.

rubocop should check every file under `test/`.

Related to #32441, #32605

`#ordinal` and `#ordinalize` now support I18n

Improve css in guide

Improve redundancy in line tasks

* [ci skip] Update links in RDOC_MAIN and remove style of word rails in README

* [ci skip] Update links in RDOC_MAIN and remove style of word rails in README

[Felipe Tovar & Rafael Mendonça França]

Fixes StrongParameters `permit!` to work with nested arrays

Add RuboCop for `assert_not` over `assert !`

Add exculude condition in rubocop.yml

Navigate edgeguides from .github template [ci skip]

Similarly to https://github.com/rails/rails/pull/32626/commits/9c3fe52f5fa9904b43bf76be13f85db57c223d0c

[ci skip] Update README and RDOC_MAIN

* Navigate prefer edgeguide over guide
* Because edgeguide is always described latest policy we have