[DirectX] Add depth/stencil buffer support

[inbelic]

This is required for testing of the SV_Depth* and SV_StencilRef semantics.

Current status; Depth/stencil buffers are already supported in Vulkan: #756.

Note: A depth/stencil attachment is always created on Vulkan. It should be decided during planning if we want to allow this to be configurable.

The first step to completion is to update this issue with a comprehensive plan.

AC:

• Implement equivalent depth buffer functionality for DirectX
• Add independent testing of functionality
• All existing tests referencing this ticket are passing for DXC and clang (where applicable)

[EmilioLaiso]

Linking #1020 as it added depth buffers to DX/MTL backends. Tests were not introduced in this PR though, so the issue can't be closed yet.