This PR adds general-purpose functions for obtaining a `Length` in
viewport units.
Previously in #3600 we had added specific variants of `w` and `h` that
took viewport units, but I think it makes more sense to just have a
primitive that can compose with any styling method that accepts a
`Length` or `Into<Length>`.
Release Notes:
- N/A
This PR increases the max height of the outline picker so that it can
take up a larger area of the screen when there are lots of results.
This behavior is similar to the way it was in Zed1.
Release Notes:
- N/A
