Previously we would never get a valid `consistent_type` as we were
trying to make the node types consistent with the initial empty type
which isn't possible.
Gains us 7 WPT tests.
Math functions like abs(), clamp(), round(), etc, can be used by
themselves in property values, without wrapping them in calc().
Before this change, we were neglecting to run calc simplification on the
generated calculation node trees. By doing that manually after parsing a
standalone math function, we score at least a couple hundred WPT points.
