[BUGFIX] Make category tree filterable for editors with category mounts

TCEFORM.pages.categories.config.treeConfig.rootUid should filter
the category tree. Non-Admin users with category mounts currently
need every child category of rootUid in their category mounts
since the rootline of rootUid is not checked against the category
mounts.

Resolves: #78274
Releases: master,8.7,7.6
Change-Id: Id02ae69111df7397207939a034ed05797eb160ad
Reviewed-on: https://review.typo3.org/54138


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>