Create an intro test for Vision inlined members

From @VincentDondain @ https://github.com/xamarin/xamarin-macios/pull/6837#pullrequestreview-279183521

> Also you have "We must inline the following 5 properties" in a bunch of places. I believe we should have a test that enforces that propagation on all the children (we definitely have that for other cases like this).

The inlined members that must go into subclasses so the bindings use the correct class_pt are the following:

https://github.com/xamarin/xamarin-macios/blob/3e3e980565113534c3db3bc88984dff1a178866f/src/vision.cs#L1355-L1381

We should create an intro test that any `VNRequest` subclass should have those properties available