Opaque nature of depth buffers not sufficiently specified

I think the opaque nature of depth buffers is not sufficiently specified.

The formats have `UNORM` and are refered to as unsigned normalized many times.

For color attachments it is nicely said what happens:

> If the color attachment has a signed or unsigned normalized fixed-point format, color values are assumed to be floating-point and are converted to fixed-point as described in Conversion from Floating-Point to Normalized Fixed-Point;

For depth buffers this is not stated (or noted it is unspecified), and instead there is bit misleading:

> If the depth test passes, the sample’s (possibly clamped) **z_f** value is conditionally written to the depth framebuffer attachment based on the `depthWriteEnable` member of `VkPipelineDepthStencilStateCreateInfo`.

Start by comparing the cited depth-buffer write wording with the specification's color-attachment conversion passage. Determine whether normalized depth formats require an explicit conversion rule or an explicit statement that the behavior is unspecified; the issue is done when the Vulkan specification resolves that ambiguity consistently.

Written by the indexing model from the issue text.