Fix guide anchor generation logic.

* Require either FIRST or LAST qualifier for "NULLS ..."
* Require whitespace before "NULLS ..."

Fix postgresql adapter #columns_for_distinct trimming whitespace it shouldn't

This could use in any translation because it's not limited to `[^a-z0-9]`.

Verify after this change, all guides still have same anchors.

[Robin Dupret & Juanito Fatas]

Fixes #16623 introduced by https://github.com/rails/rails/commit/3d5a2019bcccc6fb01bee4811ca669f4383edb51

Fix example code in Active Job guide [ci skip]

Correct AR::RecordNotFound in AJ guide rescue example [ci skip]

Use zero-padding for number_to_rounded_converter

Documentation update for form_for options

Added enqueue_at support for QueAdapter in ActiveJob

[ActiveJob] Add hook for test_framework

This is true of the first param (url_for_options),
not of the second options param which is being
documented here.

[ci skip]

Docs for all the other form tag helpers in this
file already clarify this.

[ci skip]

[ActionMailer] require activejob railtie

adding the exception RecordNotFound to UUID find #11957

Don't calculate in-place changes twice

Now that `changed_attributes` includes in place changes, we don't need
to override these methods in Active Record. Partially fixes the
performance regression caused by #16189

Implemented enqueue_at for ActiveJob's Backburner adapter

Active Job Guide: Example of config queue_name_prefix [ci skip]

Don't fight against ourselves for the default log level

Replacing an each with reduce

Define the Duration#instance_of? method

This way no new object allocation is taking place. Thanks @jeremy for
the suggestion!

Pass logging message through block.

Missing space. [CI SKIP]

This follows the good practice listed on http://guides.rubyonrails.org/debugging_rails_applications.html#impact-of-logs-on-performance

See AR::Associations for greater detail in Nested Model Forms Guide [ci skip]

[skip ci]

Patch by @bcjordan

[ci skip] Added documentation for has_and_belongs_to_many scope parameter