[FEATURE] RTE: Avoid overhead of Ext.each and Ext.iterate

Improve performance by replacing Ext.each and Ext.iterate with
standard JS for statements.

Releases: master
Resolves: #62321
Change-Id: Id17994d4deadb6786b8c8a5071928bcb38bb2407
Reviewed-on: http://review.typo3.org/33383
Reviewed-by: Stanislas Rolland <typo3@sjbr.ca>
Tested-by: Stanislas Rolland <typo3@sjbr.ca>