wgsl: Add AbstractFloat sign execution tests

[zoddicus]

Fixes #2582

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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.

[dneto0]

Thanks!

[dneto0]

nit: Does this actually need to be added? When I read the docs a couple of weeks ago I thought the actual numbers were updated by some other process at some time.

[zoddicus]

I am not aware of a process that updates them.
Are you thinking of the steps in adding_timing_metadata.md that describe using the tooling to update things instead of manually editing the file? (That is what I did)

I have updated these tests, since they are going from being a no-op .unimplemented() to actually running code, so the runtime will likely be significantly longer now.

When just fixing a bug in a test, I generally don't update the values, unless I have reason to think the estimate will change significant.

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