Look at fullest view when checking for static types in unnesting

Look at fullest view when checking for static types in unnesting

When seeing if any bound involved in a type is an uplevel reference,
we must look at the fullest view of a type, since that's what the
backends will do.  Similarly for private types. We introduce
Get_Fullest_View for that purpose.

	* sem_util.ads, sem_util.adb (Get_Fullest_View): New procedure.
	* exp_unst.adb (Check Static_Type): Do all processing on fullest
	view of specified type.