[BUGFIX] Bring back final class name cache

The class name needs to be determined through
a lookup in the implementation configuration
(AKA XCLASS).

This runtime cache was removed in favor of
a cache in the class loader. But this caching
behavior also changed due to the package management
API implementation.

Releases: 6.2
Resolves: #55024
Change-Id: I8dc101c0c04c88e531907fcfaf82e529af483e01
Reviewed-on: https://review.typo3.org/26821
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter