Update RecordNotFound exception cases to include a message with the
Model that the Record was not found in.
A warning line should look like a warning section

[ci skip]
Cleanup loaded features and constants after dependency tests.
Add a note on custom validation contexts.

The documentation on `:on` for validations was inconsistent, and most
only referenced the `:create` and `:update` contexts. I fixed those to
be consistent with the documentation on `AM::Validations.validates`,
which seemed to have the best docs.

[ci skip]
[ci skip] add guide for ActiveModel::SecurePassword
'Reversible' ->active_record_migrations [ci skip]

Reversible method documentation moved from migrations.md  to active_record_migrations.md
'Revert' ->active_record_migrations [ci skip]

Revert method documentation moved from migrations.md  to active_record_migrations.md
[ci skip] Fix some typos, normalize sentence.

Follow up of #16722.

https://github.com/rails/rails/pull/16722

also normalize all instance gained methods’ sentence.
Changes default render behavior from file to template.
form_helpers: demonstrating there is also a collection_select method in form builder
[ci skip] Fix code snippet display in Action Mailer Basics guide.
Consistently capitalize ETag.
Consistently markup etag options.
Cleaner queuing of jobs using Delayed Job
Standardize on `Rails.application` [ci skip]

This seems to be the style settled on in most of the templates.
Merge pull request #16981 from gsamokovarov/concern-docs-comment-reword

[ci skip] Reword a comment in concern's documentation
Merge pull request #15791 from zev/add_model_to_recordnotfound_message

Update RecordNotFound exception cases to include a message with the
Quick fix to address the borken build caused by #15791

This is pretty lame though, so feel free to send a PR with a better fix! ;)

cc @zev @tenderlove
Fix find_by with associations not working with adequate record

For now, we will just skip the cache when a non-column key is used in the hash.
If the future, we can probably move some of the logic in PredicateBuilder.expand
up the chain to make caching possible for association queries.

Closes #16903
Fixes #16884
No need to call to_sym here

The hash is now string-keyed, and [_]reflect_on_association calls `to_s` on the
argument anyway.