Adds support for atomic counters to the D3D11 renderer using UAV.

Bug: angleproject:1729
Test: angle_end2end_tests
Change-Id: I2904ba62644685b7d91f7475bd80a81ae414993b
Reviewed-on: https://chromium-review.googlesource.com/c/1451259
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>