angle_test_instantiate.cpp & angle_test_instantiate_apple.mm:
- Disabled metal platform selection on pre-10.13 mac devices for
Bug: angleproject:4153

Explicitly disabled tests on metal:
- DifferentStencilMasksTest.DrawWithDifferentMask
- PointSpritesTest.PointSizeAboveMaxIsClamped
- WebGL2ReadOutsideFramebufferTest.CopyTexSubImage3D

This requires the crash fix in http://crrev.com/c/1924101

Bug: angleproject:4153
Bug: angleproject:2634
Change-Id: I95046d731a8ba7414cf1a1f4b6f2940282725872
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1926389
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>