[TASK] RTE: Migrate to RequireJS

This is a follow-up to http://review.typo3.org/35131

Releases: master
Resolves: #63636
Change-Id: I35b29c2163536cae16388510f7e2268c1a5cb565
Reviewed-on: http://review.typo3.org/35132
Reviewed-by: Stanislas Rolland <typo3@sjbr.ca>
Tested-by: Stanislas Rolland <typo3@sjbr.ca>