[Ada] AI12-0339: Empty function for Aggregate aspect of Ada containers

[Ada] AI12-0339: Empty function for Aggregate aspect of Ada containers

gcc/ada/

	* sinfo.ads, sinfo.adb: The flag Box_Present can appear in
	Iterated_Element_Association nodes.
	* sem_aggr.adb (Resolve_Aggregate): Call
	Resolve_Container_Aggregate when type of context has
	corresponding aspect.
	* sem_type.adb (Covers): In Ada_2020 an aggregate is compatible
	with a type that carries the corresponding aspect.
	* exp_ch3.adb (Make_Controlling_Function_Wrappers): Do not
	create declarations and bodies for inherited primitive functions
	of null extensions that dispatch on result, when current scope
	includes an immediately visible non-overloadable homonym of the
	function.
	* libgnat/a-cborse.adb, libgnat/a-cborse.ads,
	libgnat/a-cbhase.ads, libgnat/a-cbhase.adb,
	libgnat/a-cborma.adb, libgnat/a-cborma.ads,
	libgnat/a-cbhama.adb, libgnat/a-cbhama.ads,
	libgnat/a-cbdlli.adb, libgnat/a-cbdlli.ads,
	libgnat/a-convec.ads, libgnat/a-ciorse.ads,
	libgnat/a-cihase.ads, libgnat/a-cihase.adb,
	libgnat/a-ciorma.ads, libgnat/a-cihama.ads,
	libgnat/a-cihama.adb, libgnat/a-cidlli.ads,
	libgnat/a-cidlli.adb, libgnat/a-coinve.adb,
	libgnat/a-cobove.adb, libgnat/a-cobove.ads,
	libgnat/a-convec.adb, libgnat/a-coinve.ads,
	libgnat/a-coorse.ads, libgnat/a-cohase.adb,
	libgnat/a-cohase.ads, libgnat/a-coorma.ads,
	libgnat/a-cohama.adb, libgnat/a-cohama.ads,
	libgnat/a-cdlili.ads: Add primitive function Empty for use in
	aspect Aggregate, and add corresponding body or expression
	function.