Fix segfault with 2d gizmos

[mockersf]

Objective

• Don't segfault with gizmos in 2d
• Fixes Segmentation fault when running 2d_gizmos example #8144, Fixes Segmentation Fault on OSX on main branch #8211

Solution

• Don't use depth in 2d

[tim-blackbird]

I'm glad you managed to find a fix :)

And it might make sense that this would fail since depth_stencil is None for the 2d pipeline, but in that case I figure wgpu is missing some validation logic.
@cwfitzgerald, Does what I said makes sense? Should we open an issue on the wgpu repo?

[lewiszlw]

Verified, it works for me.

[james7132]

Explanation and fix LGTM. Approving based on @lewiszlw's test.

[cwfitzgerald]

This is definitely something wgpu needs to deal with in some way, afaik it's perfectly legal to write to frag_depth without depth, so we might need to remove it when writing out the MSL or something, or update the spec.