[TASK] Resolve Todos in InheritancesResolverService

Add some comments to understand InheritanceResolverService class.
Minor refactoring of duplicated code.
Add Test for the doc example.

Resolves: #83238
Releases: master, 8.7
Change-Id: I3aed06a76b609ef78641530a19e3379f202c84ec
Reviewed-on: https://review.typo3.org/54948


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>