[lworld] RFR: 8287241: Add IdentityException to report that a value object is not valid

[ExE Boss]

On Tue, 24 May 2022 18:25:18 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

> Add class java.lang.IdentityException, when thrown indicates that an identity object was required but a value object was supplied.
> 
> Also add methods `java.util.Objects.requireIdentity(obj)` and `Objects.requireIdentity(obj, message)` to check and throw.
> 
> Updated java.lang.ref.Reference and related tests to use new exception and method.

There should probably also be a `requireIdentity(T obj, Supplier<String> messageSupplier)` overload, like there is for `requireNonNull`:
https://github.com/openjdk/valhalla/blob/eb1682287408033bf1c7738a95cc11a5d73ff7aa/src/java.base/share/classes/java/util/Objects.java#L397-L402

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PR: https://git.openjdk.java.net/valhalla/pull/696