[Ada] Ada2020: AI12-0027 Access values and unaliased component

[Ada] Ada2020: AI12-0027 Access values and unaliased component

Access values should never designate unaliased components.
This new feature is documented in AI12-0027-1.

gcc/ada/

	* sem_ch13.ads (Same_Representation): Renamed as
	Has_Compatible_Representation because now the order of the arguments
	are taken into account; its formals are also renamed as Target_Type
	and Operand_Type.
	* sem_ch13.adb (Same_Representation): Renamed and moved to place the
	routine in alphabetic order.
	* sem_attr.adb (Prefix_With_Safe_Accessibility_Level): New subprogram.
	(Resolve_Attribute): Check that the prefix of attribute Access
	does not have a value conversion of an array type.
	* sem_res.adb (Resolve_Actuals): Remove restrictive check on view
	conversions which required matching value of Has_Aliased_Components of
	formals and actuals.
	* exp_ch4.adb (Handle_Changed_Representation): Update call to
	Same_Representation.
	(Expand_N_Type_Conversion): Update call to Same_Representation.
	* exp_ch5.adb (Change_Of_Representation): Update call to
	Same_Representation.
	* exp_ch6.adb (Add_Call_By_Copy_Code): Update call to
	Same_Representation.
	(Expand_Actuals): Update call to Same_Representation.
	(Expand_Call_Helper): Update call to Same_Representation.