"Fixes the problem of concurrent populations of clustering row ranges
leading to some readers skipping over some of the rows.
Spotted during code review.
Fixes #2834."
* tag 'tgrabiec/fix-cache-reader-skipping-rows-v2' of github.com:scylladb/seastar-dev:
tests: mvcc: Add test for partition_snapshot_row_cursor
tests: row_cache: Add test for concurrent population
tests: row_cache: Make populate_range() accept partition_range
tests: Add simple_schema::make_ckey_range()
cache_streamed_mutation: Add missing _next_row.maybe_refresh() call
mvcc: partition_snapshot_row_cursor: Fix cursor skipping over rows added after its position
mvcc: partition_snapshot_row_cursor: Rename up_to_date() to iterators_valid()
mvcc: Keep track of all iterators in partition_snapshot_row_cursor
mvcc: Make partition_snapshot_row_cursor printable
(cherry picked from commit af1976bc30)
[tgrabiec: resolved conflicts]
f9864686d2