Merge pull request #16552 from untidy-hair/update_plugin_guide

[ci skip] Update plugin doc with the latest rails
use same idiom to define class method as in every other adapter.
"warning: assigned but unused variable"
Merge pull request #16554 from y-yagi/patch-2

[ci skip] config.active_record.errors_in_transactional_callbacks -> config.active_record.raise_in_transactional_callbacks
Gem `queue_classic` does not support JRuby
Skip adapter queue_classic for JRuby
Merge pull request #16556 from jonatack/patch-9

4.2 Release Notes pass [ci skip]
Merge pull request #16559 from splattael/jruby-queue_classic

Do not depend on queue_classic on JRuby
Merge pull request #16487 from jayshepherd/patch-1

Small grammar fix in pluck description
minor copy editing [ci skip]
Merge branch 'master' of github.com:rails/docrails

Conflicts:
	actionpack/lib/action_controller/metal/mime_responds.rb
	actionview/lib/action_view/vendor/html-scanner/html/sanitizer.rb
	activerecord/lib/active_record/type/value.rb
Improve custom configuration

1. Hashes can be assigned
2. We don't need a special level anymore

The method chain only works in the top level.

If users need a second level they need to assign a OrderedOptions to the
key:

    config.resque.server = ActiveSupport::OrderedOptions.new
    config.resque.server.url = "http://localhost"
    config.resque.server.port = 3000

[Rafael Mendonça França + Carlos Antonio da Silva]
Add missing AS require

`strip_heredoc` method is defined on active_support/core_ext/string
Merge pull request #16562 from arthurnn/missing_string_require

Add missing AS require
Add default .raise_in_transactional_callbacks option to template
Move TimeHelperTest to TimeTravelTest from `as/test_test.rb`
Merge pull request #16299 from sikachu/ps-safer-ac-params

Update `ActionController::Parameters` to be more secure on parameters handling
Protect against error when parsing parameters with Bad Request

Related with #11795.
Merge pull request #16536 from rails/improve-custom-configuration

Improve custom configuration
Merge pull request #16349 from jmcnevin/master

Correctly determine if migration is needed.