[lworld] RFR: 8346307: [lworld] Clarify identity vs value in Class, Objects, and document limitations of value objects [v6]

[Roger Riggs]

> Add APINote  and javadoc for IdentityException where it will be useful to know that identity or value objects are treated differently. 
> Simplified WeakHashMap javadoc updates for IdentityException. 
> Added note to System.identityHashCode to include value objects.
> Added to class javadoc for IdentityHashMap for value objects.

Roger Riggs has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains eight commits:

 - Merge branch 'lworld' into 8346307-throws-identityexception
 - Merge branch 'lworld' into 8346307-throws-identityexception
 - Merge
 - Expand javadoc reference to Reference
 - Merge remote-tracking branch 'refs/remotes/origin/8346307-throws-identityexception' into 8346307-throws-identityexception
 - Merge branch 'openjdk:lworld' into 8346307-throws-identityexception
 - 8346307: [lworld] Document WeakHashMap and other apis that may throw IdentityException
   Add APINote  and javadoc for IdentityException where it will be useful to know.
   Simplified WeakHashMap javadoc updates for IdentityException.
   Added note to System.identityHashCode to include value objects.
 - 8346307: [lworld] Document WeakHashMap and other apis that may throw IdentityException
   Add APINote and javadoc for IdentityException where it will be useful to know.
   Updated Objects.hasIdentity to return true for non-null reference to identity class; else false
   Added Objects.isValueObject to return true for non-null reference to value class; else false
   Updated tests for value objects.

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Changes: https://git.openjdk.org/valhalla/pull/1327/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1327&range=05
  Stats: 250 lines in 11 files changed: 193 ins; 14 del; 43 mod
  Patch: https://git.openjdk.org/valhalla/pull/1327.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1327/head:pull/1327

PR: https://git.openjdk.org/valhalla/pull/1327