Previously, the LibWeb bindings generator would output multiple per
interface files like Prototype/Constructor/Namespace/GlobalMixin
depending on the contents of that IDL file.
This complicates the build system as it means that it does not know
what files will be generated without knowledge of the contents of that
IDL file.
Instead, for each IDL file only generate a single Bindings/<IDLFile>.h
and Bindings/<IDLFile>.cpp.
Because we store calculations as a tree of CalculationNodes inside a
CalculatedStyleValue, instead of a tree of StyleValues directly, this
implements a create_calculation_node() method on CSSNumericValue.
CSSMathValue::create_an_internal_representation() then calls
create_calculation_node() on itself, and wraps it in a
CalculatedStyleValue.
Lots of WPT passes again! Some regressions, which are expected: `cursor`
fails a test for the same reason it fails other that set it to some
kind of numeric value: We don't distinguish between "can contain a
number" and "can accept a number by itself". This will affect any
similar properties, but overall this is a big improvement.
