Ensure correct SkSurfce::MakeFromCAMetalLayer availability.

CAMetalLayer is available on iOS versions above 8.0. However, when using the
simulator, this version is bumped up to 13.0. This is done via a separate header
altogether and there is no provision to specify simulator versions in
API_AVAILABLE. SK_API_AVAILABLE_CA_METAL_LAYER must be used to signal correct
API availability in all versions of iOS including simulators.

Change-Id: I628e3062fd9531869400dc8a29d42f96afb11d82
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/284988
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Auto-Submit: Chinmay Garde <chinmaygarde@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
2 files changed