Font features consist of a hash table of number
values, which will never change during compute,
so there is no point in recreating a new value
with a copy of the hash table, constaining the
same string->number mapping.
This commit is still way too big, but I couldn't make it smaller.
It transitions the old CSS parser to the new parser. CSS parsing is now
tokenized, everything else is probably still buggy.
We can't try to get an integer because ultimately integer getters
support the same shenanigans that numbers and percentages do with calc()
and whatnot.
