8389539: Clarify equivalence class sizing with value objects

[jddarcy]

Another update to Object.equals to better support value classes.

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• JDK-8389539: Clarify equivalence class sizing with value objects (Enhancement - P4)

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[mlbridge]

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• 00: Full (ee528aef)

[liach]

I would use the term "a single distinguishable element" instead of going into "multiple value objects" - "multiple" is an impression from the times when each constructor invocation creates a new distinguishable instance. Value objects are not necessarily constructed, either - in hotspot, you may load from a field twice and get two indistinguisable value objects, but another implementation may deduplicate them, and all these deduplication etc. are not visible to programs based on our specs.