This logic will be shared with ANGLE_get_image. Cleans up some of the
graph access logic so it can work easily with TextureVk/RenderbufferVk.

Bug: angleproject:3944
Change-Id: If069528f27b2c291d52de892c707562875b95227
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1879962
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Cody Northrop <cnorthrop@google.com>