Improve tests for GIMarshallingTests

- Add some passing tests
- Explain some skipped tests
Add failing test for GIMarshallingTests.gerror_out
Correctly map :error type
Explicitely test that errors are raised
A non-throwing function should just return any GError results
Handle non-throwing GError :out arguments
Handle (non-throwing) GError return values
Add tests for GLists of :uint32
Handle casting of :uint32 to InPointer
Handle GPtrArray arguments and return values
Add tests for other GIMarshallingTests GPtrArray functions
Add and improve tests for GType related functions in GIMarshallingTests