[BUGFIX] Memory consumption in DataHandler->processClearCacheQueue

Reduce memory consumption in DataHandler->processClearCacheQueue() for
bulk inserts by filling $tagsToClear as an associative array instead of
a normal array with array_unique()-call after each added record.

Resolves: #63615
Releases: master, 6.2
Change-Id: I1f557f435088cab3aa928ec3f44b0ded9265d7a7
Reviewed-on: http://review.typo3.org/35211
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>