Metal: Ensure helper invocations when derivatives are used Set sample coverage mask to ensure that fragment shader helper invocations are performed when derivatives are used. Fixed the following tests on Apple silicon: dEQP-GLES2.functional.texture.mipmap .2d.projected.nearest_linear_repeat .2d.projected.linear_linear_repeat .cube.projected.linear_nearest .cube.projected.linear_linear dEQP-GLES3.functional.texture.mipmap .2d.projected.nearest_nearest_mirror .2d.projected.linear_nearest_clamp .2d.projected.linear_nearest_repeat .2d.projected.linear_nearest_mirror .2d.projected.nearest_linear_repeat .2d.projected.linear_linear_clamp .2d.projected.linear_linear_repeat .3d.projected.nearest_nearest_mirror .3d.projected.linear_nearest_clamp .3d.projected.linear_nearest_repeat .3d.projected.nearest_linear_clamp .3d.projected.nearest_linear_mirror .3d.projected.linear_linear_clamp .3d.projected.linear_linear_repeat Fixed: angleproject:8443 Fixed: angleproject:7023 Change-Id: I13fc52532b94de098dcf3e9f5f02d48a6c8913c7 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5089131 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Alexey Knyazev <lexa.knyazev@gmail.com>