Summary:
Fixes https://github.com/facebook/rocksdb/issues/11742

Even after performing duty (1) ("Waiting for the next refill time"), it is possible the remaining threads are all in `Wait()`. Waking up at least one thread is enough to ensure progress continues, even if no new requests arrive.

The repro unit test (https://github.com/facebook/rocksdb/commit/bb54245e6) is not included as it depends on an unlanded PR (https://github.com/facebook/rocksdb/issues/11753)

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11763

Reviewed By: jaykorean

Differential Revision: D48710130

Pulled By: ajkr

fbshipit-source-id: 9d166bd577ea3a96ccd81dde85871fec5e85a4eb