RFR: 8314280: StructuredTaskScope.shutdown should document that the state of completing subtasks is not defined

[Alan Bateman]

This is a docs only change. The specification for StructuredTaskScope.shutdown should make it clear that the state of subtasks that are completing (with a result or exception) at around the time of shutdown is not defined. The state of a completing subtask may transition to a terminal state, it may not, as it is racing with the shutdown.

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

Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/15293/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15293&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314280
  Stats: 6 lines in 1 file changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15293.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15293/head:pull/15293

PR: https://git.openjdk.org/jdk/pull/15293