wgsl: Convert all AbstractFloat tests with non-simple errors to using f32 intervals

[zoddicus]

A number of existing tests for AF expressions were incorrectly implemented via performing the accuracy calculations as f64. These need to be converted to using the f32 interval calculations, because absolute, ULP, and inherited AF errors should be as accurate as f32.

This changes additition, cross, determinant, degrees, division, dot, fma, mix, radians, remainder, and various forms of matrix multiplication.

See https://www.w3.org/TR/WGSL/#abstract-float-accuracy for details on why this change is needed.

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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 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.

[zoddicus]

PTAL, I have broken this up into a series of different commits on the PR for easier review, but will be squash them on commit.

[dneto0]

Thanks!

[dneto0]

Thanks for these comments. They very much clarify the issue for a future reader.