[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: I74bef31fcf1f08665e51cee7efe847e32f501ef2
Reviewed-on: http://review.typo3.org/35232
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Tested-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>