This has been left unimplemented since we switched to the Skia renderer.
Now `text-decoration-style: wavy` actually paints a wavy line. :^)
We had a text-decoration test, but it only checked `solid` lines, so
I've replaced it with a modified version of the old test page from
Serenity, without the blink option, and with some thickness parameters.
I did experiment with using a `SkPath1DPathEffect` to make it repeat the
pattern for us, but I couldn't make it look good at all.
d8a73a8165