Describe the pull request

This PR implements a common descriptor management architecture by implementing VK_EXT_descriptor_buffer in the Vulkan backend. The new approach provides two central descriptor buffers at the device instance, similar to the descriptor heaps for the D3D12 backend. All related functions have been moved to the graphics device base interfaces. As descriptors are not required to have the same size, it is not possible to allocate equal chunks from the descriptor heaps. For this reason, the buffer interface has been extended with two new methods that can be used to read and write raw memory directly.

This PR also fixes two minor issues:

• Descriptor set layouts are now properly destroyed.
• The native Vulkan swap chain now uses the proper present target layout, if the D3D12 backend is not built.

ToDo

• Fix ray tracing and ray queries samples. (Non-issue, see: Potential false positive error when vertex buffer in BLAS is empty. KhronosGroup/Vulkan-ValidationLayers#10721)
• Validate samples
• Validate tests

Related issues

• Use descriptor buffers to implement descriptor management for Vulkan. #163
• Improve descriptor management. #162