[ci skip] Fix broken url in plugins guide
Merge pull request #16472 from y-yagi/patch-1

[ci skip] Fix broken url in plugins guide
users_dont_suck_but_only_we_suck_and_only_our_tests_are_order_dependent!

Calling ActiveSupport::TestCase.i_suck_and_my_tests_are_order_dependent! in AS::TestCase makes
everyone's tests order dependent, which should never be done by the framework.
Remove old setup from AS test case

This was added back in Rails 3 on
c4a6109286909c394e8c5bfc471a1eb9de245d2b, and is not being used anymore.
Fixed failing tests; Load active_job in railtie; Renamed generator to job
CHANGELOG entry for TestCase.i_suck_and_my_tests_are_order_dependent! fix
Added activejob to install.rb
Update activejob's README
Modified activejob.gemspec to match other rails gems format
use 'based on' instead of 'based off' [ci skip]
Nobody sucks so nobody should call this awful method name
Merge pull request #16476 from akshay-vishnoi/doc-changes

[ci skip] use "based on" or "based off of"
:bomb:
[ci skip] Updated where scope to conform to new style
`index_exists?` with `:name` checks specified columns.

[Yves Senn & Matthew Draper]

The column check was embodied in the defaul index name.
If the :name option was used, the specified columns were not verified at all.

Given:

```
assert connection.index_exists?(table_name, :foo_id, :name => :index_testings_on_yo_momma)
```

That index could have been defined on any field, not necessarily on `:foo_id`.
Merge pull request #16489 from tomkadwill/updating_options_to_new_style

[ci skip] Updated where scope documentation to conform to new style
[ci skip] fix spelling of override
Added ActionMailer::DeliverLater
AM, AP, AV, and AMo tests are already order_independent!
Duplicated method in the test helper