Migrated AVCompositionDebugVieweriOS to unified api

- Cast double to nfloat
- Cast nfloat to float
- Change CGContext.SetRGBFillColor to .SetFillColor
- Change CGContext.SetRGBStrokeColor to .SetStrokeColor
- Removed (Action) cast added by migration tool
- Replaced CGRect.CGSize.Height with CGRect.Size.Height (the tool might
have added .CGSize)