LibWeb: Stub out simplify_a_calculation_tree

[stelar7]

Im not sure if this is the best way of handling it, or if it should happen more like this stelar7/serenity@b83e45c

[AtkinsSJ]

Im not sure if this is the best way of handling it, or if it should happen more like this stelar7/serenity@b83e45c

I think this does need to live somewhere outside of the parser - we need to simplify the calculation at computed-value type (when it's assigned to a node) and later at used-value time. (Though for that last one, just calculating the value directly probably makes more sense, since we won't need to keep the calculation around afterwards.) See https://drafts.csswg.org/css-values-4/#calc-computed-value

I know I've kept changing my mind on calc(), which isn't helpful. It's complicated. 😅

I've looked again at the specs since talking on Discord, and I think the values and typed-om specs are compatible, which is a relief (though the typed-om spec is missing a few things that we'd need to ad-hoc ourselves). Eventually I think what we want to do is (in no particular order):

• Replace our ad-hoc CalculationResult with CSSNumericValue by implementing the add(), sub(), etc methods on it.
• Make our calculation nodes be CSSMathValue subclasses, so a calculation is some kind of CSSMathValue containing various kinds of CSSNumericValue.
• Simplification would then take a CSSMathValue (or be a method on it) and return a CSSMathValue.
• At some point we should probably add the IDL side to these types too.

So you're welcome to take on however much of that you feel like. Those first two points are probably hard to do separately. You can also try adding simplification without doing those, but it'll mean that code will need modifying later.