Add GL_NV_read_depth_stencil Bug: angleproject:4688 Change-Id: I44d5846f1ae5382b8c046e59643da4c0bf38e135 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3702356 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Auto-Submit: Constantine Shablya <constantine.shablya@collabora.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>