[BUGFIX] Fix various misbehaviors in "Broken Extension Scanner"

The "Broken Extension Scanner" has some flaws that are fixed with this
patch:

- Only one request is sent to scan all ext_localconf.php /
  ext_tables.php files, each
- ext_tables.php is only scanned if ext_localconf.php was successful,
  since those are dependent
- Protected extensions (mandatory to the system) cannot get uninstalled
- After uninstalling an extension all caches are cleared

Resolves: #89947
Releases: master, 9.5
Change-Id: I63aa7e67df9d061fded42af34c72727db629258a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/62639


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Susanne Moog <look@susi.dev>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Susanne Moog <look@susi.dev>