RFR: 8303489: Add a test to verify classes in vmStruct have unique vtables [v3]

[Alex Menkov]

> Unique vtables for classes in vmStruct data is a requirement for SA to correctly detect hotspot classes.
> The fix adds test to verify this requirement.
> 
> The test fails as expected on Windows if VM is built without RTTI (see JDK-8302817)

Alex Menkov has updated the pull request incrementally with one additional commit since the last revision:

  Chris's feedback

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12820/files
  - new: https://git.openjdk.org/jdk/pull/12820/files/ceac098b..903be28e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12820&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12820&range=01-02

  Stats: 20 lines in 1 file changed: 6 ins; 0 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/12820.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12820/head:pull/12820

PR: https://git.openjdk.org/jdk/pull/12820