* Seemlesly switch for the RichTextEditor based message composer to the plain one depending on whether formatting options are enabled or not.
* Address PR comments
* Fixes#2803 - Add extra padding at the bottom of the composer suggestions list
* Update preview test snapshots
* Update UI test snapshots
* Move ComposerToolbar files to withing the RoomScreen folder (as it's not a screen on its own)
* Switch the plain composer to NSAttributedStrings
* Enable suggestions on the plain composer
* Introduce a new `MatrixUserDisplayName` attributed string attributed and use it for mention building
* Implement mention pill rendering and sending on the plain message composer
* Fix plain composer snapshot tests
* Fix broken formatting options layout
* Add clarifying comment.