[CLEANUP] Cleanup BuilderModuleController.php

This mainly fixes CGL violations:

* import classes
* variable names must be lower camel case
* method names must be lower camel case
* intentions of blocks
* Add getBackendUserAuthentication()

Resolves: #58247
Releases: 6.2
Change-Id: I3418fc8a6b93fe23d60cc6f7c43cdfdef5dc47a2
Reviewed-on: https://review.typo3.org/29683
Reviewed-by: Oliver Klee
Reviewed-by: Nico de Haen
Tested-by: Nico de Haen