[TASK] Tests: Refactor cache Typo3DatabaseBackend

Tests of the Typo3DatabaseBackend are refactored to not depend on
initialized $GLOBALS['TYPO3_DB'] anymore, queries and quoting is
now performed to a mock object. Next to a better separation this
has the advantage of a nice speedup executing those tests.

Change-Id: I8fc23fec56a50e48f74422eac3ee4a07ed3669b9
Resolves: #56937
Related: #51436
Releases: 6.2
Reviewed-on: https://review.typo3.org/28420
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring