[BUGFIX] Allow "distinct" in select.selectFields

Add "distinct" into the whitelist of allowed select parts.

Resolves: #43114
Releases: master, 9.5
Change-Id: I8ae6561ff6067117b9d5acb6c976966fecaee96a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/38372


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Frank Nägler <frank.naegler@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Frank Nägler <frank.naegler@typo3.org>