Call ImageImpl::destroy before destroying the image source.
Call ImageImpl::destroy before destroying the image source.

egl::Image destroys the source sibling before calling the backend destroy
function.  ImageVk needs the source image to do proper clean up.

BUG=angleproject:3722

Change-Id: I110d77a9c4151166624bb953c579102ac7dab6ee
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1709752
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Commit-Queue: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle