[lworld] RFR: 8378375: [lworld] System.identityHashCode for value objects should vary by its class

[Roger Riggs]

System.identityHashCode for value instance should include a salt value that varies by class.
This improves the distribution of hashcodes for value classes with similar primitive fields.
The class hashCode is a decent salt value and is readily available.

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Commit messages:
 - Merge branch 'lworld' into 8378375-hashcode-use-class-hashcode
 - SALT for value objects is the class identityHashCode

Changes: https://git.openjdk.org/valhalla/pull/2169/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2169&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378375
  Stats: 13 lines in 1 file changed: 0 ins; 12 del; 1 mod
  Patch: https://git.openjdk.org/valhalla/pull/2169.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2169/head:pull/2169

PR: https://git.openjdk.org/valhalla/pull/2169