We can also use these maps and sets in place of `SeaHasher` because
they are also deterministic. Note that we're not swapping std's
`HashMap` and `HashSet` wholesale inside of `collections` because
on the server we need cryptographically secure collections.
ShapedLines are never wrapped, whereas WrappedLines are optionally wrapped if
they are associated with a wrap width. I tried to combine everything because
wrapping is inherently optional for the Text element, but we have a bunch of
APIs that don't make sense on a line that may wrap, so we need a distinct type
for that case.
