Add test to verify all the valid subgroup sizes work for subgroup size attribute

[Jiawei-Shao]

This patch adds an execution test to verify all the power-of-two values in [SubgroupMinSize, SubgroupMaxSize] can be used as @subgroup_size attribute in a simple compute pipeline.

Issue: #4640

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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 22d1a41):

-webgpu:shader,execution,shader_io,compute_builtins:subgroup_size_attribute:* - 6 cases, 6 subcases (~1/case)
+webgpu:shader,execution,shader_io,compute_builtins:subgroup_size_attribute:* - 36 cases, 36 subcases (~1/case)
-TOTAL: 283229 cases, 2325040 subcases
+TOTAL: 283259 cases, 2325070 subcases

[Jiawei-Shao]

@jrprice @kainino0x PTAL, thanks!

[kainino0x]

existing nit: not needed, makeBufferWithContents does it already.