[lworld] RFR: 8336390: [lworld] jdk/internal/util/ReferencedKeyTest.java fails with --enable-preview

[Roger Riggs]

ReferencedKeyTest uses Long to test the key maps.
However, with --enable-preview Long is a value class and cannot be used with Weak or Soft references.

Replace use of Long with String (an Identity class)

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Commit messages:
 - 8336390: [lworld] jdk/internal/util/ReferencedKeyTest.java fails with --enable-preview

Changes: https://git.openjdk.org/valhalla/pull/1177/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1177&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336390
  Stats: 46 lines in 2 files changed: 5 ins; 0 del; 41 mod
  Patch: https://git.openjdk.org/valhalla/pull/1177.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1177/head:pull/1177

PR: https://git.openjdk.org/valhalla/pull/1177