ada: Recognize iterated_component_association as potentially unevaluated

Routine Is_Potentially_Unevaluated was written for Ada 2012, but now we
use it for Ada 2022 as well, so it must recognize iterated component
associations (which were added by Ada 2022) as an array component
association.

gcc/ada/

	* sem_util.adb (Is_Potentially_Unevaluated): Recognize iterated
	component association as potentially unevaluated.