Canonicalization can require information that is only known after
compute time (i.e. resolved relative lengths within calcs).
This also allows us to get rid of the `had_explicit_input` flag and just
rely on whether Optional has a value
For whatever reason, this method in particular ends up failing to link
into WebContent with a subsequent change. It's small and simple, so
just inline it.
This reverts 0e3487b9ab.
Back when I made that change, I thought we could make our StyleValue
classes match the typed-om definitions directly. However, they have
different requirements. Typed-om types need to be mutable and GCed,
whereas StyleValues are immutable and ideally wouldn't require a JS VM.
While I was already making such a cataclysmic change, I've moved it into
the StyleValues directory, because it *not* being there has bothered me
for a long time. 😅
