Creates a button group of given type if it exists in any registered button group factory function.

Creates a button group of type aButtonGroupType, if it exists in any registered button group factory function, and returns a handle to the button group interface the constructed object implements. Extra required information is supplied in aCreationData. If the button group is to be added to the button group stack then this can be set in aAddToButtonGroupStack. Returns NULL if aButtonGroupType doesn't exist in any registered button group factory function.