Compiler support tracking TS keyColName for Probe MapJoin

Compiler needs to track the original TS key columnName used for MJ probedecode.
Even though we know the MJ keyCol at compile time, this could be generated by previous (parent) operators thus we dont always know the original TS column it maps to.

To find the original columnMapping, we need to track the MJ keyCol through the operator pipeline. Tracking can be done through the parent operator ColumnExprMap and RowSchema.