RFR: 8328592: hprof tests fail with -XX:-CompactStrings

[Aleksey Shipilev]

See the bug for symptoms. The tests are failing because hprof test library is confused about non-compact strings.

Additional testing:
 - [x] `serviceability/HeapDump lib-test:all` with `-XX:-CompactStrings` now pass
 - [x]  `serviceability/HeapDump lib-test:all` with `-XX:+CompactStrings` still pass

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/18394/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18394&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328592
  Stats: 19 lines in 2 files changed: 13 ins; 1 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/18394.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18394/head:pull/18394

PR: https://git.openjdk.org/jdk/pull/18394