metal: Create a global residency set, holding all allocated heaps

[MarijnS95]

gpu-allocator creates heaps on which callers can allocate ranges and create "placed" resources like textures, buffers and acceleration structures. These individual resources, or the heaps as a whole, need to be made resident on the command buffer or even globally on an entire queue.

In the previous API those heaps had to be made resident on individual command encoders with useHeap(s): (making an entire heap resident perfectly matches a bindless design, as opposed to making every individual resource -either placed on the heap or allocated separately- resident with useResource(s):). Worse, this API only applies MTLResourceUsageRead (exluding RenderTarget and ShaderWrite textures) which would disallow any resources on the heap to be written.

Now with MTLResidencySet multiple heaps can be made resident with one call, defeating the performance overhead of individually "using" all heaps on every command encoder. But without tracking this inside gpu-allocator, users of our crate still have to manually rebuild this MTLResidencySet each time they change their allocations, without knowing when gpu-allocator created or destroyed a heap.

By managing a single updated MTLResidencySet in gpu-allocator, callers can simply call .commit() on this object right before they submit command buffers referencing resources on these heaps, as long as they have the residency set attached to the queue in question or "used" on the command buffer that is being submitted. This removes all the performance overhead of repeatedly creating MTLResidencySets, which otherwise defeats the purpose of it over plain useHeap(s): call(s).