Vulkan: Only re-create pipeline on state change. This speeds up the simple perf test, but it is a very simple optimization that does not have a cache of pipelines or anything sophisticated. BUG=angleproject:1898 Change-Id: Iec126bc73bf28f8bb33662a2f70670588f010d72 Reviewed-on: https://chromium-review.googlesource.com/444850 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>