feature: add iOS popover support

[greedbell]

Example:

<Screen
  stackPresentation = 'popover'
  popoverSourceViewNativeID = 'push:pink',
  popoverSourceRect = {{
          x: 10,
          y: 10,
          width: 44,
          height: 44,
   }}
  popoverPermittedArrowDirections = {['up', 'down']}
  preferredContentSize = {{
          width: 600,
          height: 600,
    }}
  ...
/>

[osdnk]

@greedbell Please add video and resolve conflicts

[marcosrdz]

Would be awesome to have this merged.