Vulkan: Prefer driver uniforms over spec consts On hardware that's not seeing any benefit from specialization constants, this change switches to using driver uniforms to reduce the number of pipelines created. Bug: angleproject:7406 Bug: b/173636783 Change-Id: Ic1ea1b389b0b27169427643f811370943195f331 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3692270 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Charlie Lao <cclao@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>