Just the CSS property; not hooked up to any rendering behavior yet.
Currently this is implemented as a simple longhand text-wrap property,
but we'll want to rename it to text-wrap-style when we update white-space
to be a shorthand and introduce white-space-collapse, text-wrap-mode, etc.
The 'pretty' value is omitted as we have no immediate plans to implement it.
Initially, 'auto' and 'stable' will behave identically, although 'auto' could
change in future once we have higher-quality algorithms available.