Describe the pull request

This PR overhauls the binding of descriptor sets containing both, samplers and resources. This was partially supported previously, but only for the DirectX 12 backend, where it too only worked under certain circumstances, due to root parameter indices not being properly mapped across multiple descriptor tables for a single descriptor set. #163 thus temporarily removed support entirely by throwing an exception during pipeline creation, if such a scenario was encountered. This PR now addresses those issues and implements proper support for such a use case.

For the Vulkan backend, this resulted in a refactoring of the descriptor buffer implementation, as descriptor sets must be fully bound to a descriptor buffer. This is different to D3D12, where a descriptor set can (and must) be split over two descriptor heaps (for samplers and resources), which is not possible in Vulkan. Fortunately, GPUinfo reports equal memory requirements for samplerDescriptorBufferAddressSpaceSize/resourceDescriptorBufferAddressSpaceSize and descriptorBufferAddressSpaceSize over all devices that support VK_EXT_descriptor_buffer, so we can easily combine sampler and resource heaps into a single heap that binds all resource types.

Related issues

• This is a preliminary PR for implementing Add support for dynamic descriptor types and direct heap access. #164, as the default DXC behavior emits a mixed descriptor set when both ResourceDescriptorHeap and SamplerDescriptorHeap are used in a shader.