Set up prototype interface for MakeFromCAMetalLayer

Change-Id: I87b0fc76ef48c1a21498e576853a6c3b4a6a98f9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/242563
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
5 files changed