[TASK] Implement interface instead of deprecated extension of SoftReferenceIndexParser

[susannemoog]

See https://docs.typo3.org/c/typo3/cms-core/master/en-us/Changelog/master/Deprecation-94741-RegisterSoftReferenceParsersViaDI.html

Someone with more knowledge in this area should look over the changes - they were enough to get it running on my website again ;)

[CybotTM]

Done with #161