GetMappedRange never produces errors and instead returns nullptr when it
is disallowed. When in a correct state, should return a valid pointer as
much as possible, even if the buffer is an error or if the device is
lost.
Adds tests for error buffers and device loss, and modify existing tests
to not expect a device error.
Also removes some dead code in the Vulkan backend and adds a fix for
missing deallocation of VkMemory on device shutdown.
Bug: dawn:445
Change-Id: Ia844ee3493cdaf75083424743dd194fa94faf591
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/24160
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Stephen White <senorblanco@chromium.org>