Vulkan: Add a alpha to coverage test Early fragment test optimization has to be disabled if alpha to coverage is enabled. This test that the intersection between alpha to coverage test and early fragment test optimization. Bug: angleproject:5082 Change-Id: I628efc2fae7c998467e1daff4167f16fe0c28142 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2422899 Commit-Queue: Charlie Lao <cclao@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>