Add UAV format for GL_RGBA8I GL_RGBA8I is a supported image unit format, add its corresponding UAV format on D3D backend. Bug: angleproject:1987 TEST=dEQP.GLES31/functional_image_load_store_2d_store_rgba8i dEQP.GLES31/functional_image_load_store_2d_load_store_rgba8i Change-Id: Ib759f873c8629a644f85784a57ce141d3018e0c1 Reviewed-on: https://chromium-review.googlesource.com/c/1378888 Reviewed-by: Jiajia Qin <jiajia.qin@intel.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Xinghua Cao <xinghua.cao@intel.com>