sstables: Implement sstable_streamed_mutation::fast_forward_to()
sstables: Implement sstable_streamed_mutation::fast_forward_to()

Handling of forwarding is done inside mp_row_consumer, because it
allows us to filter out irrelevant data sooner and thus more
efficiently.

Becuase static row can be now skipped as well, _skip_clustering_row
was renamed to more generic _skip_in_progress.

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