[BUGFIX] Native DateTime values cannot be mapped from storage

DateTime values that are stored with an accordant (native) type
cannot be mapped correctly since a unix timestamp is expected.
The TCA configuration property 'dbType' for 'date' and
'datetime' fields reflects the non-timestamp way.

Change-Id: Ie694cf020a08ad91cc14982943b26705e5b128a9
Fixes: #46193
Releases: 6.0, 6.1
Reviewed-on: https://review.typo3.org/19450
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Steffen Ritter
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader