IsOptimizedVersion returns true if hashJoinVersion equals to HashJoinVersionOptimized.

HashJoinVersionLegacy means hash join v1.

HashJoinVersionOptimized means hash join v2.

UseHashJoinV2ForNonGAJoin is added because Hash join contains a lots of types(like inner join, outer join, semi join, nullaware semi join, etc) we want to GA these different kind of joins step by step, but don't want to add a new session variable for each of the join, so we add this variable to control whether to use hash join v2 for nonGA joins(enable it for test, disable it in a release version).