[lworld] RFR: 8336673: [lworld] TestIdentityWithEliminateBoxInDebugInfo.java fails with migrated classes

[Tobias Hartmann]

Test fails because it does not expect `==` to be a susbtitutability test for `Long` arguments with `--enable-preview`. Let's just make it the default.

Best regards,
Tobias

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Commit messages:
 - enable preview
 - 8336673: [lworld] TestIdentityWithEliminateBoxInDebugInfo.java fails with migrated classes

Changes: https://git.openjdk.org/valhalla/pull/1204/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1204&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336673
  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/valhalla/pull/1204.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1204/head:pull/1204

PR: https://git.openjdk.org/valhalla/pull/1204