RFR: 8256643: Terminally deprecate ThreadGroup stop, destroy, isDestroyed,…

[Alan Bateman]

This change terminally deprecates the following methods defined by java.lang.ThreadGroup 

- stop 
- destroy 
- isDestroyed 
- setDaemon 
- isDaemon 

The stop method has been deprecated since=1.2 because it is inherently unsafe. It is time to terminally deprecate this method so it can be removed in a future release. Thread.stop will be examined in a separate issue. 

The destroy, isDestroyed, setDaemon, isDaemon methods support the mechanism to explicitly or automatically destroy a thread group. As detailed in JDK-8252885, the mechanism to destroy thread groups is flawed and racy. Furthermore, this mechanism inhibits efforts to drop the reference from a thread group to its threads (so that thread creation, starting and termination do not need to coordinate with their thread group). These methods should be terminally deprecated so they can be degraded in a future release and eventually removed.

CSR with more information:  https://bugs.openjdk.java.net/browse/JDK-8256644

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Commit messages:
 - Update jshell class
 - 8256643: Terminally deprecate ThreadGroup stop, destroy, isDestroyed, setDaemon and isDaemon

Changes: https://git.openjdk.java.net/jdk/pull/1318/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1318&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256643
  Stats: 31 lines in 4 files changed: 28 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1318.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1318/head:pull/1318

PR: https://git.openjdk.java.net/jdk/pull/1318