Metal: Preemptively Start Provoking Vertex CmdBuffer on AMD There seems to be a bug in older AMD drivers and this appears to work around it Bug: angleproject:7635 Change-Id: I1b22e4b7d5d1ce0d405e422d08d33eeeb731050a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3877666 Reviewed-by: Kenneth Russell <kbr@chromium.org> Commit-Queue: Kenneth Russell <kbr@chromium.org>