[TASK] Indexed Search: Introduce strict types

This patch adds PHP types to all properties and methods within
EXT:indexed_search.

Resolves: #102914
Releases: main
Change-Id: If3cb7fc8af53c4bbc02781546128d23f6f1c56d8
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82632


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