Cache the value of `changed_attributes` when calling `changes_applied`

`changes_applied` calles `changes`, which will call `changed_attributes`
multiple times in a loop. This method actually performs work now, so we
should cache the results while looping over it when we know it cannot
change.
Update documentation to match change in #5942 [ci skip]
Speed up JRuby tests by improving its startup time

Emulate `jruby --dev` which improves JRuby's startup time.

See
https://github.com/jruby/jruby/wiki/Improving-startup-time#use-the---dev-flag

Follow @headius' idea and give Java more memory to reduce GC time.
[ci skip] use proper apostrophe
[ci skip] make assert messages consistent
Merge pull request #16690 from ankit1910/proper-use-of-aporstrophe

[ci skip] use proper apostrophe
Use ActiveSupport::Concern instead of the traditinal way
Quick pass through the 4.2 release notes [ci skip]

Fix a few typos and made some tiny improvements. Refs #16576.

[Zachary Scott & Robin Dupret]
Merge pull request #16682 from untidy-hair/use_activesupport_concern

Use ActiveSupport::Concern
Merge pull request #16689 from ankit1910/improve-english

[ci skip] make assert messages consistent
Added web links

Added web links to resque, delayed_job and sidekiq
Merge pull request #16695 from ericbrooke/patch-1

Added web links
Fixed find_by("sql fragment without bindings") on master

* Also duplicated find_by tests from relations_test.rb to finder_test.rb now
	that we have a completely different implementation on the class (in core.rb
	with AST caching stuff).

* Also removed a (failing) test that used mocks. Now that we have tests for the
  behavior, there's no point having another test that tests the implementation
	(that it delegates). Further, what the test was implying is nolonger true with
	the current implementation, because Class.find_by is a real method now.
Override #find_by! in core to enable AST caching
Merge pull request #16646 from sgrif/sg-perf-regression

Cache the value of `changed_attributes` when calling `changes_applied`
[ci skip] Added documentation for has_and_belongs_to_many extension parameter
Merge pull request #16697 from tomkadwill/has_and_belongs_to_many_documenting_extension_param

[ci skip] Added documentation for has_and_belongs_to_many extension parameter
[ActiveJob] Autoload adapters
Keep the first string we fetch

Otherwise, it's possible for GC to run in between, and fail the test.
Merge pull request #16613 from splattael/master

Speed up JRuby tests by improving the startup time