Rename assumptions: bounded -> finite, unbounded -> infinite

fixes #7943
fixes #5294

finite: `abs(x) < oo`
infinite: `abs(x) = oo`

- [x] decide about naming (e.g. unbounded)
- [x] change temporary variable names (e.g. bounded -> finite)
- [x] rebase to fix commit msg (bounded -> finite!)
- [x] add some references