No errors for constant property associations

[stevevestal]

OSATE will accept the following declarations. It would seem that either an error would be raised on the first property association that constant is only allowed in property sets; or else an error would be raised in the second that overriding a property earlier declared to be constant is not allowed. (It would actually be nice to do this in some cases. Perhaps the committee might let such a request slip through into AADL 2.3 as an errata.)

system Desired_Component
	properties
		Memory_Size => constant 5 MByte;
end Desired_Component;

system implementation Desired_Component.Provided_Implementation
	properties
		Memory_Size => 10 Mbyte;
end Desired_Component.Provided_Implementation;

[lwrage]

According to the standard Memory_Size cannot be overwritten in the implementation because it is marked constant in the type. I assume that the same would apply for type extension.
If a contained property association is marked constant it means that there cannot be another contained property association higher up in the containment hierarchy that overrides the property value.

[lwrage]

We need to add a validation that finds errors when overriding a constant property value that is inherited.
Instantiation needs to check if a contained property association overrides a constant property value. This tracked in a separate issue (#1447).