WorldSystem: Provide WadMapConverter with the Id1MapRecognizer to use

This is a temporary arrangement to prevent inadvertent desync with the
converter-recognized map data. Logically speaking, one should think of
the recognizer as "owned" by the converter plugin (and not MapDef).

See the comments in WadMapConverter's ConvertMapHook() for an overview
of how this system should work in the future.