Eng 6695 partial agg for ordered subquery

It seems strange to be setting this member on the m_parsedSelectStmt as a side effect of this call.
One caller (above) immediately resets it to the same value. That seems strange.
I'm not sure whether the other caller switchToOrderedInputForGroupBy really intends or needs to set it.

Do we know that this is the final plan for this statement, so it's safe to be setting properties on the statement that depend on the plan details?