[jdk21] RFR: 8309853: StructuredTaskScope.join description improvements

[Alan Bateman]

8309853: StructuredTaskScope.join description improvements

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Commit messages:
 - Backport 3661cdee1b20ab2868025637871d22bb30add6bd

Changes: https://git.openjdk.org/jdk21/pull/55/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21&pr=55&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309853
  Stats: 82 lines in 1 file changed: 54 ins; 3 del; 25 mod
  Patch: https://git.openjdk.org/jdk21/pull/55.diff
  Fetch: git fetch https://git.openjdk.org/jdk21.git pull/55/head:pull/55

PR: https://git.openjdk.org/jdk21/pull/55