[TASK] Introduce use-statement for Utility-namespace in Bootstrap

Change I12f66acef697dbec9b065edcba8ad0d8f78c4e01 broke
Bootstrap.php since there was no use-statement for the Utility-
namespace as we have in 6.1/6.2 already.

Introducing this use and shortening function-calls.

Change-Id: Idc6524d0b3b4c8c077ab00d21716dda5a2c04f0f
Related: #45834
Resolves: #50506
Releases: 6.0
Reviewed-on: https://review.typo3.org/22654
Tested-by: Stefan Neufeind
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters