Support frame buffering without descriptor overwrite

[tom-huntington]

DML owns the Uav descriptors for the input and output buffer. This means if you want to frame buffer you have to frame buffer the entire dispatchable (or else the input descriptors will be overwritten before the gpu has use the descriptor). This is wasteful as you only need to framebuffer the input and output buffers not the compute shaders and intermediate buffers (the buffers DML owns).

You could extent the API, so that the application could own the input and output descriptors rather than DML:

struct DML_BUFFER_BINDING1 {
  D3D12_GPU_DESCRIPTOR_HANDLE Descriptor;
  UINT64         SizeInBytes;
};