RFR: 8302354: InstanceKlasss init state/thread should be atomic

[Robbin Ehn]

Hi, please consider.

These states are read 'lock-less' should thus be atomic.
Also the assert setting init thread state can be stricter.

Passes t1-4

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Commit messages:
 - Initial fix

Changes: https://git.openjdk.org/jdk/pull/12542/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12542&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302354
  Stats: 15 lines in 5 files changed: 1 ins; 0 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/12542.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12542/head:pull/12542

PR: https://git.openjdk.org/jdk/pull/12542