Allow for translation of C++ references as C# byrefs

[PathogenDavid]

C++ references and C# byrefs have similar (if not identical) semantics. Right now C++ references are emitted as C# pointers which isn't as nice to work with as the C++ API would be from C++.

We should (optionally) support emitting C++ references as C# byrefs.

IE:

• ImVec2& x would be emitted as ref ImVec2 x
• const ImVec& x would be emitted either as ImVec2 x or in ImVec2 x depending on developer preference