Vulkan: GS tests that demonstrate gl_Position bugs Bug: angleproject:5478 Bug: angleproject:5479 Change-Id: If7ae7b6e0960c66dde697726381bc68c6809b3c6 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2599940 Reviewed-by: Charlie Lao <cclao@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>