Pointers to native classes should _not_ be dereferenced by C#

Actual behavior

The GdipDeleteRegion method gets a friendly overload that takes ref GpRegion instead of GpRegion*.
This might be fine, except that GpRegion* should never be dereferenced, since it's a pointer to a class on the C++ side. The struct defined in the metadata has an IntPtr field, but unlike HWND where that is just a copyable opaque value, GpRegion (and other GDI+ structs) actually represent C++ classes, and the 'field' in these structs is misleading. What would really be at that memory location is the first field in the C++ class, so copying around the struct in C# would lead to data corruption as anyone that re-takes the pointer to the struct would expect the full class fields where the struct is, and they wouldn't be there.

Expected behavior

Any extern methods that take a pointer to a native object should not have friendly overloads that replace the pointer with ref or other modifiers.

Start by tracing generation of the GdipDeleteRegion extern method and the metadata that describes GpRegion*. Check how pointer parameters are converted into friendly C# overloads. Done means native-object pointers no longer receive ref or other dereferencing overloads, with generated signatures or tests confirming the behavior.