This should let the Vulkan back-end only need to sync the Image data
once before we use them.

Bug: angleproject:3427
Change-Id: I8c6e8794e861f855bddbf651997351e8415e3479
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1602912
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>