[jdk17u-dev] RFR: 8307068: store a JavaThread* in the java.lang.Thread object after the JavaThread* is added to the main ThreadsList

[Goetz Lindenmaier]

I backport this for parity with 17.0.9-oracle.

I had to resolve almost all of this change.
One of the reason is that JavaThread is in thread.cpp in 17, 
but in a file of it's own in head.
All differences should be in the context, though. 
The code could be applied unchanged.

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Commit messages:
 - Backport ceca198ef21b9003492b456d87180d2f48774f73

Changes: https://git.openjdk.org/jdk17u-dev/pull/1587/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1587&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307068
  Stats: 29 lines in 4 files changed: 20 ins; 5 del; 4 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1587.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1587/head:pull/1587

PR: https://git.openjdk.org/jdk17u-dev/pull/1587