[Ada] Simplify aspect processing with membership tests

[Ada] Simplify aspect processing with membership tests

gcc/ada/

	* sem_ch13.adb (Analyze_One_Aspect): Detect aspect identifiers
	with membership tests.
	(Check_Aspect_At_End_Of_Declarations): Likewise.
	(Freeze_Entity_Checks): Likewise; a local constant is no longer
	needed.
	(Is_Operational_Item): Similar simplification for attribute
	identifiers.
	(Is_Type_Related_Rep_Item): Likewise.
	(Resolve_Iterable_Operation): Detect names with a membership
	test.
	(Validate_Independence): Replace repeated Ekind with a
	membership test.