RFR: 8302781: CDS archive heap not reproducible after JDK-8296344

[Ioi Lam]

[JDK-8296344](https://bugs.openjdk.org/browse/JDK-8296344) changed the order of when `oopDesc::identity_hash()` is called for the archived heap object.

This one-liner fix restores the order, so that we initialize the `identity_hash` part of the archived object headers predictably.

Please see [my comment in the JBS report](https://bugs.openjdk.org/browse/JDK-8302781?focusedCommentId=14561163&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-14561163) for details.

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Commit messages:
 - 8302781: CDS archive heap not reproducible after JDK-8296344

Changes: https://git.openjdk.org/jdk/pull/12628/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12628&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302781
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12628.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12628/head:pull/12628

PR: https://git.openjdk.org/jdk/pull/12628