Fix assignment of AInt to u32 in the expression generator

[amaiorano]

Apply the same fix that was made for AFloat to AInt when emitting the value assignment WGSL. Otherwise, if
globalTestConfig.unrollConstEvalLoops is true, as it is on Windows, then we emit invalid WGSL because we index an array of AInts with a runtime index, forcing concretization, which results in an assignment of i32 to u32. The fix is to do as was done with AFloat: we emit direct assignments of the literal values into the output array. Also made sure we don't emit the array of values in this case, as it's unused.

This fixes 'webgpu:shader,execution,expression,unary,ai_assignment:*' tests that were failing on Windows.

Issue: #1644

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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.)

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.

[ben-clayton]

Thanks!

[amaiorano]

Thanks!

I'm still not used to GitHub. I had replied "Thanks!" to your suggetions, but those got lost when I resolved them...