via KHR_image_base and ANGLE_metal_texture_client_buffer

Bug: angleproject:5763
Change-Id: I4d4a88cfbb77d8b7508b787c7fec44073d3b11b0
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2757811
Commit-Queue: Le Hoang Quyen <le.hoang.q@gmail.com>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>