[CLEANUP] Improve code style of DatabaseRecordList

* adjust docheaders
* improve readability by introducing linebreaks
* use typesafe comparison where possible
* remove unnessessary full qualified class names

Resolves: #58293
Releases: 6.3
Change-Id: Iae277008d6baeb63304c2fb4a5d057019c5de9fc
Reviewed-on: https://review.typo3.org/29708
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn