Add more operation tests for transient attachment

[beaufortfrancois]

This PR adds more operation tests for transient attachment as requested in https://issues.chromium.org/issues/462468372

Issue: #4509

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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 in the test tree.
• Test descriptions allow a reader to "read only the test plans and evaluate coverage completeness", and accurately reflect the test code.
• Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
• Helpers and types promote readability and maintainability.

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

[github-actions]

Results for build job (at 23daa71):

+webgpu:api,operation,render_pass,transient_attachment:increasing_attachments_count:* - 1 cases, 1 subcases (~1/case)
+webgpu:api,operation,render_pass,transient_attachment:overlapping_transient_attachments:* - 1 cases, 1 subcases (~1/case)
-TOTAL: 285738 cases, 2343922 subcases
+TOTAL: 285740 cases, 2343924 subcases