Make sure that spring is loaded in development only

This will fix the regression added on
b068e20b.

See tests added at ff08d31e to a better understanding about the problem

This will avoid false positives where caching? is nil and should be
false

before the application

This test is a regression test to
b068e20b that changed the load order of
Action View initializers.

Retain ActionPack dependency on ActionView. Fixes #12979.

polymorphic belongs_to association with touch: true updates old record correctly

Example: Given you have a comments model with a polymorphic commentable
association (e.g. books and songs) with the touch option set.
Every time you update a comment its commentable should be touched.
This was working when you changed attributes on the comment or when you
moved the comment from one book to another. However, it was not working
when moving a comment from a book to a song. This is now fixed.

Set `i18n.enforce_available_locales` before any other configuration option.

Discoverd by #13175.

docs: Replace an unpleasant grammatical construct.

[ci skip]

Add Application#message_verifier method to return a message verifier

It is an application global verifier that can be used to generate and
verify signed messages.

See the documentation of ActiveSupport::MessageVerifier for more
information.

Escalate missing error when :raise is true in translate helper, fix regression introduced by security fix.

Before ec16ba75,
ActionView::Helpers::TranslationHelper#translate has raised errors with
specifying options[:raise] to true.

This should work by this fix:

     begin
       t(:"translations.missing", raise: true)
     rescue I18n::MissingTranslationData
       p :hello!
     end

No need to do this in railtie as AM depends on AV either way