KIP-617 — Allow Kafka Streams State Stores to be iterated backwards

Accepted Kafka 2.7 Streams

Adds `backwardRange()`, `backwardAll()`, and `backwardFetch()` methods to `ReadOnlyKeyValueStore`, `ReadOnlyWindowStore`, and `ReadOnlySessionStore` in Kafka Streams for reverse-order iteration. All existing store iteration APIs return results in ascending order; there is no way to iterate from newest to oldest or in reverse key order without materializing all results in memory.

Details