Vulkan: Optimize VBO state changes. Also has some minor optimizations for the front-end. 12% improvement on the Vulkan VBO change test. Bug: angleproject:3014 Change-Id: I38e1a8194edfc14bfe57424be348cb9688e928f4 Reviewed-on: https://chromium-review.googlesource.com/c/1369286 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>