'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.
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.
Remove internal options from query string of paths

Fixes #17057
Improve welcome page css and table cell aignments.
Merge pull request #17024 from buddhamagnet/amend-welcome-page

Amend welcome page
:nail_care: the CSS
Remove unused code
rails-html-sanitizer is now the default

Also add to upgrading guide a notice about the deprecated sanitizers
No need to install the deprecated_sanitizer gem

It is not being used in our tests
Merge pull request #17058 from eval/issue-17057

Remove internal options from query string of paths
Keep the original implementation to not having to allocate new objects
No need CHANGLOG entry for a bug in a non released version

[ci skip]
Ensure named path params are symbols (Fixes #16958)
Merge pull request #16966 from why-el/symbolize-path-params

Ensure named path params are symbols (Fixes #16958)
[ci skip] Remove reference to config.threadsafe! in guides/configuriing.md