[Ada] Ongoing work for unnamed and named container aggregates

[Ada] Ongoing work for unnamed and named container aggregates

gcc/ada/

	* sem_aggr.adb (Resolve_Iterated_Component_Association): New
	procedure, internal to Resolve_Container_Aggregate, to complete
	semantic analysis of Iterated_Component_Associations.
	* exp_aggr.adb (Expand_Iterated_Component): New procedure,
	internal to Expand_Container_Aggregate, to expand the construct
	into an implicit loop that performs individual insertions into
	the target aggregate.