Marker annotation for value based types.

Types marked with this annotation have the following properties:

• After their construction is done, they are immutable data holders, and their identity are not used.
• The type properly implements the Object.hashCode() and Object.equals(Object) contract.
• Instances of the type may be deduplicated if they equal. This means that if two instances equal, then they can be replaced with a single instance without affecting the code in any way.

This annotation may be used by the build content serialization code to deduplicate objects, to reduce the size of the written file.