[jdk17u-dev] RFR: 8303489: Add a test to verify classes in vmStruct have unique vtables

[Goetz Lindenmaier]

I backport this to improve testing in 17u

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Commit messages:
 - Backport f9aadb943cb90382a631a5cafd0624d4e8a47789

Changes: https://git.openjdk.org/jdk17u-dev/pull/2926/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=2926&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303489
  Stats: 180 lines in 2 files changed: 178 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/2926.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/2926/head:pull/2926

PR: https://git.openjdk.org/jdk17u-dev/pull/2926