scylla-gdb.py: add pretty-printer for nonwrapping_interval<dht::ring_position>
scylla-gdb.py: add pretty-printer for nonwrapping_interval<dht::ring_position>

The patch adds a generic pretty-printer for `nonwrapping_interval<>`
(and `nonwrapping_range<>`) and a specific one for `dht::ring_position`.
Adding support to clustering and partition ranges is just one more step.

Signed-off-by: Botond Dénes <a584fa4d75a0a85d721f44fb6e06315a2853b0b6@scylladb.com>
Message-Id: <20201014054013.606141-1-a584fa4d75a0a85d721f44fb6e06315a2853b0b6@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla