[Ada] Move rewriting of boxes in aggregates from resolution to expansion

[Ada] Move rewriting of boxes in aggregates from resolution to expansion

gcc/ada/

	* exp_aggr.adb (Initialize_Record_Component): Add assertion
	about one of the parameters, so that illegal attempts to
	initialize record components with Empty node are detected early
	on.
	(Build_Record_Aggr_Code): Handle boxes in aggregate component
	associations just the components with no initialization in
	Build_Record_Init_Proc.
	* sem_aggr.adb (Resolve_Record_Aggregate): For components that
	require simple initialization carry boxes from resolution to
	expansion.
	* sem_util.adb (Needs_Simple_Initialization): Remove redundant
	paren.