vulkan: add handle type for arbitrary vulkan handles

vulkan: add handle type for arbitrary vulkan handles

Serve two purposes:
1. refcounting of vulkan handles with associated destruction.  When
   combined with the trash list, the user can ensure destruction at
   the correct time according to the vulkan rules.
2. avoids polluting our API with 32-bit vs 64-bit integer/pointers
   differences as exposed through the vulkan API.  on 32-bit, vulkan
   non-dispatchable handles are 64-bit integers and on 64-bit, they
   are pointers.