[BUGFIX] Do not inject non-singleton class into singleton

BackendConfigurationManager must not inject an instance of
QueryGenerator as the latter is not a singleton.
Instead create a local instance of QueryGenerator when it is needed.

Releases: master
Resolves: #48544
Change-Id: If58f3a5c9c6a1003a0301bd2d68622ee8ccba843
Reviewed-on: https://review.typo3.org/50033


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Thomas Hohn <thomas@hohn.dk>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Reviewed-by: Jigal van Hemert <jigal.van.hemert@typo3.org>
Tested-by: Jigal van Hemert <jigal.van.hemert@typo3.org>
Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>