RFR: 8311775: [TEST] duplicate verifyHeapDump in several tests

[Yi Yang]

This is a follow-up patch of #13667. verifyHeapDump is duplicated in several tests, this patch tries to consolidate them into one method.

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Commit messages:
 - 8311775: [TEST] duplicate verifyHeapDump in several tests

Changes: https://git.openjdk.org/jdk/pull/15202/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15202&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8311775
  Stats: 154 lines in 7 files changed: 25 ins; 110 del; 19 mod
  Patch: https://git.openjdk.org/jdk/pull/15202.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15202/head:pull/15202

PR: https://git.openjdk.org/jdk/pull/15202