Optimize VAO bindings. This CL makes the XFB binding tracking WebGL-only. That will speed up VAO binding changes in non-WebGL considerably. Also has a few inline micro-optimizations that may not have a large effect. Bug: angleproject:6371 Change-Id: Ib0a26a3b956dcd6ff78626e5cd6514b46270d882 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3170116 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>