Audit TypedArray allocations

[kainino0x]

I audited all of the TypedArray allocations I could find (I searched for /\dArray\(/ and ".slice("). I didn't measure a speedup from these changes, but the resulting code is a little more tidy.

Added comments to all of the places that I determined did not need any changes.
I also looked at expectGPUBufferRepeatsSingleValue, which has a few allocations, but I didn't attempt to profile anything there, as there's O(1) allocations there for the entire operation. It might have some unnecessary memory copying, but I don't think suspect it's that much.

Issue: None

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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.

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