[jdk17] RFR: 8269096: Add java.util.Objects.newIdentity method [v5]

[Roger Riggs]

> Add java.util.Objects.newIdentity to supply a unique object with identity.
> This is a replacement code can be used today for the traditional new Object() idiom, which will be deprecated under Project Valhalla.
> Refer to [JEP 401: Primitive Objects (Preview)](https://openjdk.java.net/jeps/401) for background.

Roger Riggs has updated the pull request incrementally with one additional commit since the last revision:

  Add test synchronizing on return value of Objecst.newIdentity()

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Changes:
  - all: https://git.openjdk.java.net/jdk17/pull/112/files
  - new: https://git.openjdk.java.net/jdk17/pull/112/files/eef1029c..f99d0846

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk17&pr=112&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=jdk17&pr=112&range=03-04

  Stats: 12 lines in 1 file changed: 12 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk17/pull/112.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17 pull/112/head:pull/112

PR: https://git.openjdk.java.net/jdk17/pull/112