To centralise logic to be more consistent, and to have smarter logic
which avoids just following newline format from input, preventing
smushing HTML elements (like list elements) next to eachother

With controller routes.
Don't consider this as a security issue, since the filtered URLs
by that validation are very likely to be blocked by browser security
or CSP, and there's a level of assumed privilege to the users that
are able to create such attachments links already.

Closes #6093

New HTML to Plaintext handling

- Updated tag values endpoint to use query param instead of path
  argument, so a better range of values can be provided (including those
  with slashes).
- Updated image gallery example request to align with docs use changes.

API:  New tag endpoints

Used for comments and descriptions.
Also updated shortcut handling that we're not registering shortcuts for
edits which can't use the related formatting types.

For #6003

WYSIWYG: Added inline code support to minimal editor

Added reference to new community rules page where sensible.

Permissions: Started addition of revision-view permission