intel/fs: Fix src and dst types of LOAD_PAYLOAD ACP entries during copy propagation.
The ACP entries created by copy propagation to track the implied copies of LOAD_PAYLOAD instructions don't model the behavior of LOAD_PAYLOAD correctly, since (as of 41868bb6) header moves are implicitly retyped to UD and the destination of non-header copies implicitly uses the same type as the corresponding source, even though the ACP entries created for such copies could incorrectly represent a type conversion, which can lead to mis-optimization of the program.
According to Marcin, this fixes the func.mesh.ext.workgroup_id.task.q0 crucible test.