Pre-existing PUA characters in data cause SDE

If data contains Unicode PUA characters, these cause the Infoset Outputter to convert the RemapPUACharDetected into an SDE.

We can't get away with this. We need to tolerate PUA characters in data and have them either cause a ParseError, or just tolerate them. (Or have a switch to choose between those modes) 

This was discovered by fuzz testing. 

If the existence of PUA characters means the data is gibberish, then perhaps the parser is speculating down a path that should be backtracked. We need a parse error in that case. 

If the existence of PUA characters is acceptable, then we need no error at all from them.