hgiMetal: Enable depth bias for line primitives could lead to rendering issues

[lilike-adsk]

Is this issue known? On MacOS with Metal, we spotted some rendering issues when apply depth bias for line primitives. E.g., when depth bias is enabled in the pipeline, and we draw triangle primitives in first pass, then draw line primitives in second pass with the previous color & depth buffers, we found the lines occluded by triangles became visible, see below.

Ignore the depth bias setting for line primitives by adding a primitive type check can produce expected result: https://github.com/PixarAnimationStudios/OpenUSD/blob/release/pxr/imaging/hgiMetal/graphicsPipeline.mm#L441

BTW, seems Metal doesn't support setdepthbias API for line primitives: https://developer.apple.com/documentation/metal/mtlrendercommandencoder/setdepthbias(_:slopescale:clamp:)

USD version: 25.08.