Do not implement feature with custom code, but use existing feature to
create search_abstract field.
Also execute DataProcessing in AbstractIndexer, not in TcaTableService,
to affect all current available indexers, not only some.
Also this is the place to be.
* To support further configuration, specific to identifiers / tables.
* E.g. mapping and boost configuration should be possible.
* Adjust docs and settings.
* Adjust tests and code.
* Add typoscript option which TYPO3 tables should be processed and which
should not be processed.
* Respect new optiion in hook.
* Also add necessary tests.
* Remove old no longer needed tests for hook.