RFR: 7903411: JOL: Rework Model64 to include comp ref/class attributes

[Aleksey Shipilev]

This is cleaner than having the duplicate classes.

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jol/pull/39/files
 Webrev: https://webrevs.openjdk.org/?repo=jol&pr=39&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903411
  Stats: 260 lines in 7 files changed: 7 ins; 227 del; 26 mod
  Patch: https://git.openjdk.org/jol/pull/39.diff
  Fetch: git fetch https://git.openjdk.org/jol pull/39/head:pull/39

PR: https://git.openjdk.org/jol/pull/39