CSSTransformComponents hold other CSSStyleValues as their parameters. We
want to be able to create internal representations from those parameters
without them caring if they would be valid when directly assigned to the
property.
This is a temporary solution to make transform functions work. To be
completely correct, we need to know what is allowed in that context,
along with value ranges - a combination of the contexts we create when
parsing, and when computing calculations. For transform functions, this
doesn't matter, as there's no limit to the range of allowed values.
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.
A lone CSSUnitValue can now be converted to a dimension StyleValue of
the relevant type, as long as the property allows that type. If the
value is out of the allowed range, it's wrapped in calc().
There are a few failing tests still, involving setting a negative
percentage and expecting to read the computed value as 0. Those also
fail in Chromium, and a similar negative-length test expects a negative
computed value (not 0), so this appears to be an incorrect test.
Also, we regress some of the `cursor` tests. This is because our "does
property X accept type Y?" code is too naive: `cursor` is defined to
accept "number [-∞,∞]" in the JSON, and that value range is used when
clamping the result of calculations or interpolation. But because that
entry is there, we think a single number is a valid value for `cursor`.
Solving this generally is a larger task than I want to take on right
now. :^)
