Load system types from referenced mscorlib
Use untyped int for enums in unmanaged callsites

By using untyped integers instead of typed integers in the unmanaged
callsites, we allow monolinker to keep the exact set of enums that are
used by the user. Without this, we’d have to keep every single enum in
place to avoid missing type exceptions.

This does not affect the public signatures or the generated code in any
way.
Enabled symbol generation; minor code cleanup
Regenerated bindings