Small Action View Overview edits [ci skip]

Some small grammar and readability edits
Define the Duration#instance_of? method

Since Duration is extending from ProxyObject which extends itself from
BasicObject, the Duration object doesn't respond to the #instance_of?
method. Thus, the #method_missing hook get triggered, delegating the
method to its `value` attribute.

However, Rubinius' #eql? definition relies on #instance_of?, thus this
will equal to true with a Fixnum (since its `value` attribute is a
Fixnum) while it should not.

The previous behavior was wrong anyway, no matter the implementation.
Grammar pass

[ci skip]

Add improvements from @eileencodes [skip ci]
Preparing for 4.2.0.beta1 release
provide a builder for form labels to customize wrapping around I18n content
Added enqueue_at support for QueAdapter in ActiveJob

* Added inline job runner for Que in test/support
* Updated QueAdapter to support enqueue_at
Upgrade guide pass. [CI SKIP]
Merge pull request #16607 from tgxworld/upgrading_guide_pass

Upgrade guide pass. [CI SKIP]
[ci skip] Clarify Action Mailer/Active Job usage note
Merge pull request #16612 from loganhasson/master

[ci skip] Clarify Action Mailer/Active Job usage note
Make text consistent in help text of rails server and console commands.
Guide fix. [CI SKIP]

Related: https://github.com/rails/rails/pull/16607
adding the exception RecordNotFound to UUID find
[ci skip] Added documentation for has_one scope parameter
Merge pull request #16615 from tgxworld/guide_fix

[ci skip] Grammar fixes for upgrade guide from 4.0 to 4.1
Merge pull request #16617 from tomkadwill/added_has_one_scope_documentation

[ci skip] Added documentation for has_one scope parameter
Merge pull request #16204 from jonatack/patch-7

Fix minor typos and improve grammar and code formatting
Merge pull request #16271 from alol/action-view-overview-guide-tweaks

Small Action View Overview guide grammar and readability tweaks
Add change to ActionView Notable changes [ci skip]
Merge pull request #16621 from Calyhre/patch-1

Update documentation, Add change to ActionView Notable changes