Remove implicit conversion operator from RString to const char*

This is required for the RString to std::string migration.

Mostly automated from https://github.com/aeubanks/rewriter/blob/main/c_str.cc, with some manual intervention required for fixing up `a + b.c_str()` to `(a + b).c_str()`.

Added some overloads for some common global functions like sm_crash to reduce the number of changes required here.

src/NotesLoaderBMS.cpp

@@ -1332,7 +1332,7 @@ bool BMSChartReader::ReadNoteData()
 		if( channel == 3 ) // bpm change
 		{
 			unsigned int bpm;
-			if( sscanf(obj.value, "%x", &bpm) == 1 )
+			if( sscanf(obj.value.c_str(), "%x", &bpm) == 1 )
 			{
 				if( bpm > 0 ) td.SetBPMAtRow( row, measureAdjust * (currentBPM = bpm) );
 			}