[TASK] Use external Core Projects workspaces and version as Git submodules

Part 1/2

Change-Id: I13ba0ff933510e5ee83fc719fb87933555ac3e70
Resolves: #26581
Reviewed-on: http://review.typo3.org/1947
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader
Reviewed-by: Steffen Gebert
Tested-by: Steffen Gebert
Reviewed-by: Stefan Neufeind