Image view is used by glTexSubImage*, glCopySubImage* and
glCopySubTexture*.
This fixed some failed WebGL tests that make use of IOSurface.

Bug: angleproject:4846
Bug: angleproject:2634
Change-Id: Iebcf840fdc1be2794feab766957b5848a361a63c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2356107
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>