Incrementally select sstables from sstable set using token
in ascending order.
For leveled strategy, it returns all sstables that belong
to current interval. For other strategies, it just return
all sstables from the set.
Useful for compaction which needs all sstables that overlap
with key being currently compacted to calculate maximum
purgeable timestamp.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>