[BUGFIX] Avoid str_replace(..., null) in AbstractMenuContentObject

PHP 8.1 emits E_DEPRECATED if second argument to
str_replace() is null. Adapt a null coalescence
and add a cast to string for TSFE->page['uid']
in AbstractMenuContentObject to avoid this.

Change-Id: Iafcf027471b976b160db768b4ada4a9535190319
Resolves: #95773
Releases: master
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/71971


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>