Vulkan: use supported composite alpha Try VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR first, if not supported, try VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR. Fail if it is not supported either. BUG=angleproject:2314 Change-Id: I875a60f7b51b9880da2d2916d602a6e7e8ca479f Reviewed-on: https://chromium-review.googlesource.com/882320 Commit-Queue: Yuly Novikov <ynovikov@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>