The layout in the PackedAttachmentOpsDesc only have 5 bits, not enough
for raw VKImageLayout enums. This change will store vk::ImageLayout
which are ANGLE defined and packed for 5 bits and able to handle the
extension bits of VKImageLayout.

Bug: b/153885625
Change-Id: Ida268a974094188d8aeee39c61019eef30a60507
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2153845
Commit-Queue: Charlie Lao <cclao@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>