postInclude for transforms using multiple SGs

For transforms using multiple StoreGates -- e.g. FastChain_tf.py with pile-up -- we need to point to the correct instance to retrieve correctly hard-scatter and pile-up events.

This postInclude configures SimHitToolBase-derived objects to use the OriginalEvent_SG collection for hard-scatter events by overriding the AthAlgTool::EvtStore property.

Depends on !31175 (merged) for MuonHitTestTool-derived classes to return successfully.

Closes ATLASSIM-4458