Async Query and ValueGeneration for Redis

Implementing the AsyncQuery method with some changes to RedisDatabase to conflate the methods used to return object[]'s from the underlying database. Enabled NorthwindAsyncQueryTests.

Also implemented GetNewCurrentValueAsync() on the RedisSequenceValueGenerator plus updated tests for that.
Do you want me to pull IQueryProvider down into EF core so that any provider can use it? Or replicate that setup in Redis?