Moving from gfx-hal to ash

[tsahyt]

Some time ago, gfx-hal was deprecated in favour of wgpu-hal since it only functioned as an abstraction layer to build wgpu on anymore. Unfortunately, for this project this meant that our hardware abstraction layer is stranded. Originally gfx-hal was picked in order to support multiple graphics APIs across several platforms. I don't deem this as important anymore. Supporting "only" Vulkan should be plenty, and the project was never tested on anything other than Vulkan to begin with.

Moving to ash should provide the lowest friction, since gfx-hal closely mirrored the Vulkan API. In the process it would also be worth looking into moving to a dedicated allocator library, and deprecating our custom allocators.