Refactor immediate operation test to drop dependency on StorageBuffer…

[shaoboyan091]

…sInFragmentStage

greggman@ pointed out that the previous immediates operation tests relies on StorageBuffersInFragmentStage, which will reduce the cover rate of the devices. (#4558 (comment))

Remove usage of StorageBuffersInFragmentStage and directly rendering result out to do operation test

Issue: #

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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.

[Copilot]

Pull request overview

This PR refactors the immediate-data operation tests to avoid relying on maxStorageBuffersInFragmentStage (especially in compatibility mode) by switching render-path verification from fragment-stage storage buffer writes to reading back an rgba32uint render target.

Changes:

• Removed the compatibility-mode skip logic tied to StorageBuffersInFragmentStage.
• Split pipeline creation into compute (storage-buffer output) vs render (fragment vec4u color output to rgba32uint) paths.
• Added a unified runAndCheck helper that validates results via buffer readback (compute) or texture readback (render).

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[github-actions]

Results for build job (at 5821c0f):

 Test case/subcase counts did not change.