Surbhi-Vijay

[VL] Support map_concat spark function

11

Adds support for `map_concat` spark function as part of #4039 Added supporting test case and updated documentation

[VL] TPCDS Performance drop after new operator "VeloxAppendBatches"

16

### Backend VL (Velox) ### Bug description We have observed performance drop in TPCDS runs after the patch #6009. Top regressing Queries -------------------------------------------- QueryId New runtime Previous Runtime query64 50712...