[lworld] RFR: 8255396: [lworld] locking breaks oopDesc is_flatArray/is_nullfreeArray type checks

[David Simms]

Added unlocked test and fallback to klass

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Commit messages:
 - 8255396: [lworld] locking breaks oopDesc is_flatArray/is_nullfreeArray type checks

Changes: https://git.openjdk.java.net/valhalla/pull/238/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=238&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255396
  Stats: 36 lines in 2 files changed: 33 ins; 1 del; 2 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/238.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/238/head:pull/238

PR: https://git.openjdk.java.net/valhalla/pull/238