RFR: 8307068: store a JavaThread* in the java.lang.Thread object after the JavaThread* is added to the main ThreadsList [v6]

[Daniel D. Daugherty]

> A small fix to store a JavaThread* in the java.lang.Thread object after the JavaThread*
> is added to the main ThreadsList. Also adds the following:
> - `java_lang_Thread::thread_acquire()`
> - `java_lang_Thread::release_set_thread()`
> 
> And uses them on an as-needed basis.

Daniel D. Daugherty has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:

 - Merge branch 'JDK-8307067' into JDK-8307068
 - Merge branch 'JDK-8307067' into JDK-8307068
 - dholmes CR - update comments and switch from java_lang_Thread::set_thread() to release_set_thread().
 - Merge branch 'JDK-8307067' into JDK-8307068
 - Forgot to checkpoint the use of java_lang_Thread::thread_acquire(thread_oop) in ThreadsListHandle::cv_internal_thread_to_JavaThread().
 - dholmes CR - follow the foo_acquire() and release_set_foo() convention;
   revert a comment change and reformat.
 - 8307068: store a JavaThread* in the java.lang.Thread object after the JavaThread* is added to the main ThreadsList

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/13723/files
  - new: https://git.openjdk.org/jdk/pull/13723/files/6e6dd0a3..f3a7a9e5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13723&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13723&range=04-05

  Stats: 69279 lines in 798 files changed: 59166 ins; 4592 del; 5521 mod
  Patch: https://git.openjdk.org/jdk/pull/13723.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13723/head:pull/13723

PR: https://git.openjdk.org/jdk/pull/13723