Add more tests for mixing up depth and color attachments

[kainino0x]

Replaces an existing small test with proper ones with control cases and more formats.

Issue: No bug, I just wrote these to make sure our implementation was correct because

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Requirements for PR author:

• All missing test coverage is tracked with "TODO" or .unimplemented().
• New helpers are /** documented */ and new helper files are found in helper_index.txt.
• Test behaves as expected in a WebGPU implementation. (If not passing, explain above.)
• Test have be tested with compatibility mode validation enabled and behave as expected. (If not passing, explain above.)

Requirements for reviewer sign-off:

• Tests are properly located.
• Test descriptions are accurate and complete.
• Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
• Tests avoid over-parameterization (see case count report).

When landing this PR, be sure to make any necessary issue status updates.

[github-actions]

Results for build job (at 1acb0a1):

+webgpu:api,validation,render_pass,render_pass_descriptor:color_attachments,depth_stencil_format:* - 7 cases, 11 subcases (~2/case)
-webgpu:api,validation,render_pass,render_pass_descriptor:attachments,color_depth_mismatch:* - 1 cases, 1 subcases (~1/case)
+webgpu:api,validation,render_pass,render_pass_descriptor:depth_stencil_attachment,color_format:* - 5 cases, 7 subcases (~1/case)
-TOTAL: 287982 cases, 2362149 subcases
+TOTAL: 287993 cases, 2362166 subcases