Improve get-buildings to work with Google buildings from source.coop

[cholmes]

The google buildings cng distro on source is done quite similar to the overture one (indeed was the start of those experiments), and ideally the get-buildings tool would work with it just as easily. There may only be small tweaks needed to get it 'working' - the likely thing that's needed is to optimize the google buildings dataset with the learnings from overture. The biggest one is setting the row group size.