ada: Fix support of Default_Component_Value aspect on derived types

ada: Fix support of Default_Component_Value aspect on derived types

The support of the Default_Component_Value aspect on derived constrained
array types is broken because of a couple of issues: 1) the derived types
incorrectly inherit the initialization procedure of the ancestor types
and 2) the propagation of the aspect does not work for constrained array
types (unlike for unconstrained array types).

gcc/ada/

	* exp_tss.adb (Base_Init_Proc): Do not return the Init_Proc of the
	ancestor type for a derived array type.
	* sem_ch13.adb (Inherit_Aspects_At_Freeze_Point): Factor out the
	common processing done on representation items.
	For Default_Component_Value and Default_Value, look into the first
	subtype to find out the representation items.