RFR: 7903523: JOL: heapdumpstats should not assume JDK 8

[Aleksey Shipilev]

There is a problem in heapdumpstats: it uses the "current VM model" for HotspotLayouter, but sets JVM version as 8. Which means it could actually fail if run on modern JDK.

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Commit messages:
 - Adjust
 - Fix
 - Fix

Changes: https://git.openjdk.org/jol/pull/47/files
 Webrev: https://webrevs.openjdk.org/?repo=jol&pr=47&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903523
  Stats: 27 lines in 2 files changed: 23 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jol/pull/47.diff
  Fetch: git fetch https://git.openjdk.org/jol.git pull/47/head:pull/47

PR: https://git.openjdk.org/jol/pull/47