Fixes STI when 2+ levels deep.

PR #14052 Added a regression where it was only looking for methods in one
level up, So when the method was defined in a 2+ levels up the
inheritance chain, the method was not found as defined.
only write the jar if the response isn't committed

when streaming responses, we need to make sure the cookie jar is written
to the headers before returning up the stack. This commit introduces a
new method on the response object that writes the cookie jar to the
headers as the response is committed.  The middleware and test framework
will not write the cookie headers if the response has already been
committed.

fixes #14352
use the body proxy to freeze headers

avoid freezing the headers until the web server has actually read data
from the body proxy.  Once the webserver has read data, then we should
throw an error if someone tries to set a header

Conflicts:
	actionpack/lib/action_controller/metal/live.rb
require actions rather than create_file

thor's create_file seems to have a circular dependency on itself when
used with our constant loading stuff.

fixes #14319
Fix probs in sections 5.6 and 5.9; [ci skip]
Force sass-rails ~> 4.0.2 to avoid sprockets compatibility error

See https://github.com/rails/sass-rails/issues/191 for more information
Match the whole string
Take in consideration guides CHANGELOG
Merge pull request #14329 from pch/digestor-lookup-fix

Ensure LookupContext in Digestor selects correct variant
Fix the resolver cache and stop mutating the lookup_context

Before we had a bug in the resolver cache so the disable_cache were not
working when passing options to find
Merge pull request #14373 from schneems/schneems/jdbc-ar-2

Allow custom JDBC urls
Obey `validate: false` option for habtm

Fixes #14383.
Remove deprecation on active_support/core_ext/class/attribute_accessors requires. Appropriate to keep this, users don't care that the implementation got unified.
Clarify AV::Digestor.digest method signature docs and deprecation warning
Let COMMAND_WHITELIST be an Array, not a String
Remove changelog for 7dfbd91b0780fbd6a1dd9bfbc176e10894871d2d since the refactoring no longer affects users after 7a5601c432d3906cc6ab853b3316e76a162f75d1
fix `number_to_percentage` with `Float::NAN`, `Float::INFINITY`.

Closes #14405.

This is a follow-up to 9e997e9039435617b6a844158f5437e97f6bc107 to restore
the documented behavior.

Conflicts:
	actionview/CHANGELOG.md
`where.not` adds `references` for `includes`.

Closes #14406.

Conflicts:
	activerecord/CHANGELOG.md
Merge pull request #14090 from Fortisque/kevin/stream_error_in_main_thread_if_not_committed

re-raise error if error occurs before committing in streaming
Merge pull request #14395 from arthurnn/fix_mailer_preview_test

Fix MailerPreview broken tests