This function is supposed to provide the positions of handles defined in GetCustomHandles(). These positions will be shown on screen when the bar constraints are edited. If a position for a handle isn't provided, that handle will not be represented on screen while edit constraints.
This function is called when edit constraints command is lunched or during edit constraints after a constraint was changed and the curve calculation was done.
bool GetHandlesPosition( RebarHandlePositionData handlePositionData )