[graphite] Add Vulkan BackendTexture creation and deletion methods; unit tests

* Add VulkanAlloc member attribute to BackendTexture such that allocations can be freed when client calls for destruction

Change-Id: I382730cc2b920a741b9dc76b4b8bf5ba355dbeac
Bug: b/237423350
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/754316
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
Auto-Submit: Nicolette Prevost <nicolettep@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
9 files changed