Add IsNative & fix multi-domain support

This pull has two commits and deprecates pull https://github.com/Monobjc/monobjc/pull/405.

1. Add IsNative type marking (requires the related pull https://github.com/Monobjc/monobjc-tools/pull/23).
2. The second commit builds on IsNative to fix multi-domain support using tokens for name mangling.