clustering_ranges_walker: Generalize to work on position ranges
clustering_ranges_walker: Generalize to work on position ranges

It will include the static row by default. This will allow simplifying
users, which work with position ranges already.

duarten/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,avikivity/scylla,duarten/scylla,duarten/scylla,scylladb/scylla