[BUGFIX] Page module: Respect connected mode during drag & drop

This patch adjusts the drag and drop handling on the page module.
Localized content element can't get moved anymore when they are in
connected mode. Languages without a `l18n_parent` may be freely
moved.

Resolves: #83470
Related: #66540
Releases: master, 8.7
Change-Id: I7dcb61279d4bfeb094dcb0e2fbffd416da9c787b
Reviewed-on: https://review.typo3.org/55453


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Armin Vieweg <armin@v.ieweg.de>
Tested-by: Armin Vieweg <armin@v.ieweg.de>
Reviewed-by: Reiner Teubner <rteubner@me.com>
Tested-by: Reiner Teubner <rteubner@me.com>
Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Reviewed-by: Michael Oehlhof <typo3@oehlhof.de>
Tested-by: Michael Oehlhof <typo3@oehlhof.de>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>