Expand cases where intermediary results can be streamed between operators

[cswinter]

There are a lot of cases where intermediary results could be streamed between operators, but aren't. One example is inability to stream from operators that produce a full output. There are probably some low hanging fruit, but proper solution is more involved and will need to revisit the overall design to solve this better, probably moving the graph partitioning from QueryExecutor to QueryPlanner to allow insertion of additional operators to aid streaming data.