[BUGFIX] Allow workspace preview inside another rootline

The rootline for page view now depends on the webmounts of the workspace
the preview link was generated on and not the webmounts the beuser, who
generated the preview link, is at the moment of calling the preview
link.

Resolves: #83547
Releases: master, 8.7
Change-Id: I53c8d45260b79c4d5679f00084fe81b502668ee7
Reviewed-on: https://review.typo3.org/55341


Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>