RFR: 8299934: LocalExecutionControl replaces default uncaught exception handler

[Jan Lahoda]

The JShell's `LocalExecutionControl` set the global default uncaught exception handler, causing problems to external code that might rely on it (even if only for logging/debugging purposes).

The proposal here is to do what the bug is suggesting, and only handling the exception inside the `ThreadGroup` that JShell creates. The patch does not strive to do further changes to how the exception handling is done.

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

Commit messages:
 - 8299934: LocalExecutionControl replaces default uncaught exception handler

Changes: https://git.openjdk.org/jdk/pull/12982/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12982&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299934
  Stats: 179 lines in 2 files changed: 165 ins; 10 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/12982.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12982/head:pull/12982

PR: https://git.openjdk.org/jdk/pull/12982