[BUGFIX] Attach CKEditor instance to RteLinkBrowser Modal, so it can be found

Previously if the RteLinkBrowser was called from a CKEditor instance that
is within an extra iframe, the CKEditor instance could not be found.
Attaching it directly to the Modal fixes this.

Resolves: #81929
Releases: master, 8.7
Change-Id: I384fc946ed671c12b1e82732f0418a347ee9f01e
Reviewed-on: https://review.typo3.org/53555


Tested-by: TYPO3com <no-reply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>