RFR: 8321940: Improve CDSHeapVerifier in handling of interned strings

[Ioi Lam]

The PR fixes the CDSHeapVerifier so that it no longer warns about interned strings that are not referenced by any of the archived heap object graphs. Please see the bug report for more details.

Tests: tiers 1-4, builds-tier5

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Commit messages:
 - added comments
 - 8321940: Improve CDSHeapVerifier in handling of interned strings

Changes: https://git.openjdk.org/jdk/pull/17102/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17102&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321940
  Stats: 36 lines in 1 file changed: 6 ins; 30 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/17102.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17102/head:pull/17102

PR: https://git.openjdk.org/jdk/pull/17102