Integrate with ANGLE

[jeremyfa]

ANGLE now supports GLES 3.0 with both DirectX 11 (windows) and Metal (ios/mac).

It seems like a good time to use it within Ceramic because:

• It would mean Ceramic apps targeting iOS or Mac would use Metal and not depend on deprecated OpenGL anymore
• Ceramic apps on windows could also run over DirectX 11 instead of OpenGL, ensuring wider compatibility and stability on that OS

These benefits, without changing the current backend for Clay, which is already compatible with GLES 3.0 spec!