1. The xfb counter buffer barrier issued was wrong, following a typo in
   the spec.  This barrier is now correctly issued using the usual
   barrier APIs.
2. A mechanism was added to automatically pause/resume transform
   feedback when a program pipeline needs to be rebound.  This is
   incorrect as it misses the xfb counter buffer barrier.  The render
   pass is broken instead if transform feedback is active/unpaused and
   the program pipeline is changed.
3. The transform feedback counter buffers are now disposed of when
   transform feedback is ended.  This avoids an unnecessary barrier that
   this change would have otherwise incurred (and hence render pass
   break) in Manhattan which repurposes the same transform feedback
   object.

Bug: angleproject:5528
Change-Id: I1ffe8b4b8975645ba43afd70e9cdbb0765529da5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2651647Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>