Consolidate `ActiveRecord::TestCase` and `ActiveSupport::TestCase` in AR test cases

Fixes #26122

add more array methods to straight delegation to speed up calling them

Clarify and fix typos in autoloading disabled section

It's tough for people without the knowledge of where the `get` and
friends integration test helpers are defined to find documentation
for them. Add a link to the main integration test documentation.

* Give the section a header to distinguish it from the general doc.
* Replace backticks with + signs to fit SDoc.
* Use double quoted strings.
* Clarify how `parsed_body` works — it doesn't depend on `as` anymore.

The Guides section about autoloading being disabled was slightly confusing
(#24724) and didn't directly reference the removed feature by name
(config.autoload_paths) making it much harder for someone to search the upgrade
guides for a mention or serendipitously find it via a Google search when running
into autoloading issues.

I also fixed some confusing turns of phrase and a missing word.

/cc @vipulnsward @jvanbaarsen

Fix the documentation for configuring `enable_fragment_cache_logging`…

- It is Action Controller config, not Action View.

Ensure app/mailers is removed when skipping action-mailer

Closes #26145

Add documentation about `ActiveSupport.on_load`

[ci skip]

This commit adds some docs that explain how `LazyLoadHooks.on_load` method
works.

Use `ActiveRecord::TestCase` rather than `ActiveSupport::TestCase` in AR test cases

Make cache max-age durations self-explanatory

Pass over changelogs

They are not part of the public API

Update example in Http::Headers object to use `.from_hash`

When initializing an `ActionDispatch::Http::Headers` object it takes a request object (Rails 5) whereas before it took a hash (Rails 4.x) but the documented example still shows a hash given to the constructor (due to commit 34fa6658) so this is just a documentation change to use the new `from_hash` method introduced in that earlier commit.

Ensure values are strings before calling gsub

[ci skip] Fix the wrong ActionCable documentation in the guide.

[ci skip] Add documentation to Parameter Encoding

Fix unsafe query generation risk.

Redo of CVE-2012-2660, CVE-2012-2694 and CVE-2013-0155

CVE-2016-6317

Creating a new Topic class instead of class_eval for the existing one

Fix warning: ambiguous first argument

Many helpers mark content as HTML-safe without escaping double quotes -- including `sanitize`. Regardless of whether or not the attribute values are HTML-escaped, we want to be sure they don't include double quotes, as that can cause XSS issues. For example: `content_tag(:div, "foo", title: sanitize('" onmouseover="alert(1);//'))`

CVE-2016-6316

since it affects another test `ReflectionTest#test_read_attribute_names`

Address #26099

add missing require rake

In ff8035df, require rake is deferred.
Therefore, it is necessary to require rake even `Engine::CommandsTasks.

Fix actionview test failure