This replaces the SDL-based system and should allow Metal to work on iOS.
OpenGL and raster will render but there's no touch input yet.
Bug: skia:8737
Change-Id: I863accc47f0e1781192d567dbe54d1e321c3cd2e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/231561
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
