MuonSTGC_CnvTools: const fixes
Preparing to make methods of IMuonRdoToPrepDataTool const.
Adjust sTgcRdoToPrepDataTool* so that its interfaces may be made const. Also enable thread-safety checking. The old pre-MT sTgcRdoToPrepDataTool is declared as not thread-safe, as it has some mutable state, while the mutable state is removed from sTgcRdoToPrepDataToolMT. sTgcRdoToPrepDataToolCore is now abstract and is removed from the entries list.