expose WorkflowBuilderM, convert expr3

- need better names
push types around a bit
convert expr1
convert expr2
mergeSt (generating old names for now)
convert groupBy/reduce
convert objectConcat

This makes some of the planner tests fail (finally), by turning some
lEft/rIghts into __tmp0/__tmp1
convert remaining cases in WorkflowBuilder
(failing) test for lpBoundPhase