[lworld] RFR: 8336029: [lworld] Rename Objects.isIdentity() to hasIdentity()

[Roger Riggs]

Rename Objects.isIdentity() to hasIdentity()
Remove java.util.Objects.isValueObject and replace its use with !hasIdentity(). 
Align the WeakHashMap WeakValuePolicy default with that of java.lang.Reference. 
Namely, throw IdentityException unless the WeakHashMap is created with a different policy. 
WeakHashMapPolicy is a unsupported experimental API.

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Commit messages:
 - 8336029: [lworld] Rename Objects.isIdentity() to hasIdentity()

Changes: https://git.openjdk.org/valhalla/pull/1163/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1163&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336029
  Stats: 39 lines in 7 files changed: 0 ins; 17 del; 22 mod
  Patch: https://git.openjdk.org/valhalla/pull/1163.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1163/head:pull/1163

PR: https://git.openjdk.org/valhalla/pull/1163