Rename `mosaic-runtime` to `mosaic-ui`?

[JakeWharton]

It's basically our :compose:ui + :compose:foundation. I don't think a UI vs. foundation split is meaningful for TUI.

However, separately, I do think we want a suite of opinionated, high-level UI akin to Material.

[JakeWharton]

Need to do a redirection pom for this. Gotta find somewhere that I've done that in the past to copy...

[JakeWharton]

I think I might flip-flop on the UI vs. foundation split. Mirroring their module hierarchy gives me an easy way to think about what goes where. Will see...