[BUGFIX] Reload page tree if `extendToSubpages` flag changes

Resolves: #83052
Releases: master, 8.7
Change-Id: I9d86c38f8d1749583e154bd52c77b168d20af7dc
Reviewed-on: https://review.typo3.org/54709


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>