Fix build warnings
```
build/mac/mobile/ReplayKit/RPScreenRecorder.g.cs(113,22): warning CS0628: 'RPScreenRecorder.RPScreenRecorder(IntPtr)': new protected member declared in sealed class
build/mac/full/ReplayKit/RPScreenRecorder.g.cs(113,22): warning CS0628: 'RPScreenRecorder.RPScreenRecorder(IntPtr)': new protected member declared in sealed class
```
which still happens even if we disable XM in `main` :|
Added generator test based on Whitney's test case from github issue
ref: https://github.com/xamarin/xamarin-macios/issues/9065