[TASK] Reduce JavaScript dependency in workspace module

The workspace module in the backend has a check and dependency to
the page module in the top frame. To ease debugging of this
backend module in a separate browser process, this dependency is
encapsulated since JavaScript errors are thrown.

Resolves: #57176
Releases: 6.2
Change-Id: I79b4d79ad23d89a70014602d4a04360f709fcab5
Reviewed-on: https://review.typo3.org/28632
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader