Cannot group-by MV column with transformation in projection

[egalpin]

Assuming that myMVdateTimeCol is an MV column of type LONG, the following will fail with a NullPointerException (root cause: ProjectionOperator is used rather than GroupByOperator, where ProjectionOperator which eventually causes a call to FixedByteMVMutableForwardIndex#readDictIds which throws UnsupportedOperationException from the default impl on the MutableForwardIndex interface).

SELECT 
  TODATETIME("myMVdateTimeCol", 'e:HH:mm:ss', 'UTC') as myTransformedVal,
  count(1) as _count
FROM 
  myTable 
GROUP BY 
  myTransformedVal

However, if the same query is executed without TODATETIME in the projection, it succeeds.

[egalpin]

This actually just requires that there be MV variants of the transforms. I'll open a PR next week to add a few that I'm interested in.