DRILL-6322: Lateral Join: Common changes - Add new iterOutcome, Operatortypes, MockRecordBatch for testing
Added new Iterator State EMIT, added operatos LATERA_JOIN & UNNEST in CoreOperatorType and added LateralContract interface
Implementation of MockRecordBatch to test operator behavior for different IterOutcomes. a) Creates new output container for schema change cases. b) Doesn't create new container for each next() call without schema change, since the operator in test expects the ValueVector object in it's incoming batch to be same unless a OK_NEW_SCHEMA case is hit. Since setup() method of operator in test will store the reference to value vector received in first batch
This closes #1211
