[TASK] Namespacing: Use-statement for common classes like GeneralUtility

Change-Id: I43d6ef559b0b46e6302ea891b4d39501a99423a6
Resolves: #49745
Releases: 6.2
Reviewed-on: https://review.typo3.org/22041
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn