DRILL-1077: OperationStats enhancements —
Add setLongStat and setDoubleStat to set metrics directly.
Remove shared HashTableMetrics class
Add ResizeTime for hash aggregate and hash join.
Not all RootExec should report the metrics in SenderStats. Break up into RootExec specific MetricDefs.
Add BYTES_SENT metric for all RootExec
Rename N_SENDERS to N_RECEIVERS
