Provide "committed resource" semantics in HAL

[kvark]

Primary motivation is getting advantage of vk-mem by @gwihlidal in our Vulkan backend. The new API entry points for buffers and images could return BoundXxx right away.

Implementing in D3D11/D3D12 and Metal is also going to be straightforward.

[grovesNL]

Is there a way we could make these optional so users could opt-in? i.e. thinking about the rendy-memory case where memory allocation is managed at the HAL abstraction level, not per backend.

Maybe we could have an optional feature and expose entry points through a HAL extension?

[kvark]

@grovesNL I think in this case we can just non-optionally expose the extra (2) entry points. If the user uses rendy-memory, they are just simply not using the new entry points. The only downside for them is dragging the vk-mem dependency.

[grovesNL]

Right, it seems a bit unfortunate to always include the additional dependency (mostly since it requires building a C++ project).

[kvark]

Now that I think of it, we don't have to include this dependency. We'll get the cleanest solution by having vk-mem dependency as optional (off by default), and just allocate a memory chunk per object (ourselves) if those new entry points are used without the dependency enabled. Hopefully, nobody would depend on this behavior in critical code ;)