Switch from SceneKit to Metal

[robomex]

The app can experience degradation issues causing AR objects to "swim," i.e. expected placement of AR objects lags behind camera movement.

Presently, SceneKit is used to drive the XRViewer ARKit experience – but I don't believe SceneKit allows control of when the video & specific frames are rendered.

Switching to Metal would allow tighter coupling/synchronizing manipulation of frames. While synchronizing frames may cause sporadic & temporary reductions in framerate, a switch to Metal would ultimately lead to a more consistent AR experience. Ideally, a switch to Metal will reduce "swim," improve the presence of AR objects, and afford additional customization in the future.