RFR: 8288497: add support for JavaThread::is_gc_barrier_detached()

[Daniel D.Daugherty]

A trivial fix to add support for JavaThread::is_gc_barrier_detached() which allows
us to add checks to detect failures like:

    JDK-8288139 JavaThread touches oop after GC barrier is detached
    https://bugs.openjdk.org/browse/JDK-8288139

This fix along with the fix for JDK-8288139 has been tested in Mach5 Tier[1-8].
There are no related failures in Mach5 Tier[1-7]; Mach5 Tier8 is still running.

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

Commit messages:
 - 8288497: add support for JavaThread::is_gc_barrier_detached()

Changes: https://git.openjdk.org/jdk19/pull/20/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk19&pr=20&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8288497
  Stats: 31 lines in 4 files changed: 22 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jdk19/pull/20.diff
  Fetch: git fetch https://git.openjdk.org/jdk19 pull/20/head:pull/20

PR: https://git.openjdk.org/jdk19/pull/20