This is the first commit in a series to enable atomic counter buffers.

Adds support for atomic counters to the GLSL->HLSL translator using
RWByteAddressBuffer.

Bug: angleproject:1729
Test: angle_end2end_tests

Change-Id: I3b7e08f9256dc9bdbcc02ad8910040f2bc14aeac
Reviewed-on: https://chromium-review.googlesource.com/c/1291329
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>