[css-values-4] Properly handle simplification of sum nodes containing negated sum nodes #13020

[Calme1709]

Closes #13020

A WPT test already exists in the form of css/css-values/calc-nesting-002.html

[tabatkins]

Looks good to me. Didn't think of this, but yes, pushing a negate into a sum makes perfect sense for simplification purposes.

Looks like Firefox is failing this test with an odd transformation - it pushes the Negate inward, but then further transforms the min() into a max() with negated arguments, which isn't supported in the spec.

Afaict, Safari is failing the test because it actually faithfully follows the spec, including for Product simplification: in this case (1 * (min(...) - 10px)), none of the simplification cases apply (it's got two children, one of which is a number and the other is a Sum, but that Sum does not contain only numeric values). Chrome (and Firefox) are simplifying the case regardless, just in different ways - Chrome is turning it into Sum(Negate(Min(...)), 10px), while Firefox, as I say above, is turning it into Sum(Max(...), 10px).

I'll open an issue about this latter transform.