[Vulkan] Add support for depth textures

[s-perron]

Introduce the Depth32 data format to define a depth texture.
Tests are added for GatherCmp and SampleCmp in Texture2D, which use the
depth textures.

The depth texture are add in the Vulkan backend only.

[Keenuts]

Added the test-all so we see results on other devices (didn't knew about this tag until recently)

[s-perron]

@tex3d @bogner As discussed in the HLSL meeting last tuesday. This adds depth textures, which are required on the Vulkan API side when doing a SampleCmp and GatherCmp. I do not know how DirectX works, so I didn't implement it. I want to make sure that DX can work with this before moving forward.

[s-perron]

@bogner FYI.

[bogner]

@bogner FYI.

Looks reasonable. I'll attempt to implement the DX side this week.