[BUGFIX] Uninitialized properties in DebuggerUtility

DebuggerUtility::var_dump() is commonly used to debug PHP classes.

We recommend hardening PHP classes by using typed properties in PHP
classes. Previously uninitialized properties resulted in a PHP exception
when passing the class instance into DebuggerUtility::var_dump.

Uninitialized properties will not be processed by
DebuggerUtility::var_dump anymore. Instead a label "uninitialized"
indicates that it has not been initialized at the time of debugging.

Resolves: #98519
Releases: main, 11.5
Change-Id: Ifbb9fd4d0de2e6214ab4b876b04302b2adaf6d2a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75981


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