PDBs reveal that these functions are also used in winspool.drv, but not imported from spoolss.dll to retain the client/server architecture.
As winspool.drv highly benefits from the MarshallUp* functions, I put them in a source file shared between spoolss.dll and winspool.drv.
The added API Tests cover my testing and all implemented features.
One more item done from https://reactos.org/wiki/Printing !
This may get more applications to work which previously called into the WINE-generated stubs (that throw an exception).
It also improves debug logs when the "winspool" debug channel is enabled. With such detailed debug logs, we may get an idea which winspool APIs need to be implemented sooner than others.