UI/text scaling information for toolkits

UI toolkits do not have a way to query environment for the preferred text and UI size, aside from a blunt integer "scale factor" in wl_output.

This makes it hard to achieve aesthetically pleasing desktop look and leads to horrible hacks like fractional scaling that ruin any chance for crisp text rendering.

This issue does not have answers (yet), but is intended to works as a Schelling point for scaling discussions:

<pq> dottedmag, so if you can't find an open issue or MR in wayland-protocols repo for it,
     it might be a good idea to open one, so things stop relying on hearsay and vague memories of irc discussions.