RFR: 8256320: ZGC: Update zDebug to support UseCompressedClassPointers

[Stefan Karlsson]

Update debugging script to support compressed klass pointers.

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Commit messages:
 - 8256320: ZGC: Update zDebug to support UseCompressedClassPointers

Changes: https://git.openjdk.java.net/jdk/pull/1198/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1198&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256320
  Stats: 6 lines in 1 file changed: 5 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1198.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1198/head:pull/1198

PR: https://git.openjdk.java.net/jdk/pull/1198