This allows the Vulkan back-end to avoid storing a reference to
the VkDevice. This will extend to all the Vulkan object handle wrapper
types.

BUG=angleproject:1684

Change-Id: I3a98e94bc171ca27f225ce57996c3fdf9581e6e1
Reviewed-on: https://chromium-review.googlesource.com/424229
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>