[Ada] Part of implementation of AI12-0212: container aggregates

[Ada] Part of implementation of AI12-0212: container aggregates

gcc/ada/

	* aspects.ads: Add Aspect_Aggregate.
	* exp_aggr.adb (Expand_Container_Aggregate): Expand positional
	container aggregates into separate initialization and insertion
	operations.
	* sem_aggr.ads (Resolve_Container_Aggregate): New subprogram.
	* sem_aggr.adb (Resolve_Container_Aggregate): Parse aspect
	aggregate, establish element types and key types if present, and
	resolve aggregate components.
	* sem_ch13.ads (Parse_Aspect_Aggregate): Public subprogram used
	in validation, resolution and expansion of container aggregates
	* sem_ch13.adb
	(Parse_Aspect_Aggregate): Retrieve names of primitives specified
	in aspect specification.
	(Validate_Aspect_Aggregate): Check legality of specified
	operations given in aspect specification, before nane
	resolution.
	(Resolve_Aspect_Aggregate): At freeze point resolve operations
	and verify that given operations have the required profile.
	* sem_res.adb (Resolve): Call Resolve_Aspect_Aggregate if aspect
	is present for type.
	* snames.ads-tmpl: Add names used in aspect Aggregate: Empty,
	Add_Named, Add_Unnamed, New_Indexed, Assign_Indexed.