RFR: 7008: Agent should properly support Class and Thread

[Marcus Hirt]

Also fixes various issues and tests.

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Commit messages:
 - Formatting
 - Temporary pre-merge commit

Changes: https://git.openjdk.java.net/jmc/pull/192/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=192&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-7008
  Stats: 476 lines in 14 files changed: 342 ins; 53 del; 81 mod
  Patch: https://git.openjdk.java.net/jmc/pull/192.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/192/head:pull/192

PR: https://git.openjdk.java.net/jmc/pull/192