[TASK] Follow-up to TCA refactoring

The patch adapts some minor nitpicks raised during review
of the main TCA patch. Most changes are comments together
with a small restriction to Configuration/TCA/*.php files
for the first cache layer and an according test adaption.

Change-Id: Idc9daead910b4ab0cbf60e7f031450efa1f68928
Resolves: #45927
Related: #45767
Releases: 6.1
Reviewed-on: https://review.typo3.org/18543
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn