[lworld] RFR: 8245646: [lworld] LW3 Reduce impact of IdentityObject on metaspace

[Frederic Parain]

Please review these changes for JDK-8245646.

This is not a new feature, just an optimization to reduce the number klass arrays containing only `IdentityObject`
begin allocated in metaspaces.

Thank you,

Fred

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Commit messages:
 - Implement shared class array containing IdentityObject

Changes: https://git.openjdk.java.net/valhalla/pull/57/files
 Webrev: https://webrevs.openjdk.java.net/valhalla/57/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8245646
  Stats: 35 lines in 4 files changed: 33 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/57.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/57/head:pull/57

PR: https://git.openjdk.java.net/valhalla/pull/57