wgsl: Add AbstractFloat round execution tests

[zoddicus]

Fixes #2509

---

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.

[github-actions]

Previews, as seen when this build job started (1425a63):
Run tests | View tsdoc

[github-actions]

Previews, as seen when this build job started (5a0f388):
Run tests | View tsdoc

[dneto0]

I think the "large int value" case is not exercised the way it was intended.

[dneto0]

This is a reinterpret cast, so this generates -0.0 in f64.

I don't think that's what you mean.

[dneto0]

The point of 2766 was to test integers that are larger in magnitude than can fit inside the mantissa bits. So for f64 that would be something in excess of 2** 53 ish.

[zoddicus]

Correct, thanks for catching this.

[zoddicus]

arg... I updated the unittests, but not the CTS test itself 😮‍💨

[zoddicus]

Updated

[github-actions]

Previews, as seen when this build job started (097b3d9):
Run tests | View tsdoc

[zoddicus]

@dneto0 PTAL, I think this should be fixed now

[jiangzhaoming]

Looks good to me, thanks

I have addressed the concerns, but they are OOO for a week, so cannot confirm