[BUGFIX] Ensure webmounts in list module are calculated only once

When using the backend search the list module is fetching the list of
PIDs to recursively look for every single TCA table.

A runtime cache is added in order to only look up this information once
per request.

Resolves: #84869
Releases: master, 8.7
Change-Id: Iad9af42a5ba88324da1f23fc354847bc96d9331d
Reviewed-on: https://review.typo3.org/56805


Reviewed-by: Stephan Großberndt <stephan.grossberndt@typo3.org>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Daniel Gorges <daniel.gorges@b13.de>
Tested-by: Daniel Gorges <daniel.gorges@b13.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>