[ty] introduce multiline pretty printer (#19979)
Requires some iteration, but this includes the most tedious part --
threading a new concept of DisplaySettings through every type display
impl. Currently it only holds a boolean for multiline, but in the future
it could also take other things like "render to markdown" or "here's
your base indent if you make a newline".
For types which have exposed display functions I've left the old
signature as a compatibility polyfill to avoid having to audit
everywhere that prints types right off the bat (notably I originally
tried doing multiline functions unconditionally and a ton of things
churned that clearly weren't ready for multi-line (diagnostics).
The only real use of this API in this PR is to multiline render function
types in hovers, which is the highest impact (see snapshot changes).
Fixes https://github.com/astral-sh/ty/issues/1000
