DRILL-6323: Lateral Join - Refactor, fix various issues with LATERAL: a)Override prefetch call in BuildSchema phase for LATERAL, b)EMIT handling in buildSchema, c)Issue when in multilevel Lateral case schema change is observed only on right side of UNNEST, d)Handle SelectionVector in incoming batch, e) Handling Schema change, f) Updating joinIndexes correctly when producing multiple output batches for current left&right inputs. Added tests for a)EMIT handling in buildSchema, b)Multiple UNNEST at same level, c)Multilevel Lateral, d)Multilevel Lateral with Schema change on left/right or both branches, e) Left LATERAL join f)Schema change for UNNEST and Non-UNNEST columns, g)Error outcomes from left&right, h) Producing multiple output batches for given incoming, i) Consuming multiple incoming into single output batch