RFR: 8368249: HttpClient: Translate exceptions thrown by sendAsync

[Volkan Yazici]

Ensure `HttpClient::sendAsync` translates every operational failure to an `IOException` as per specification.

`tier1-2` passes with the proposed changes.

**Context:** The parent issue, [JDK-8364733], reports that `HttpClient::sendAsync` leaks exceptions which do not extend from `IOException`, and this violates the method's specification. The [JDK-8367067] (#26876) sub-task improved issues around exceptions thrown by request body publishers – which triggered the first encounter with this problem. This PR (and its associated sub-task) is aimed to end this saga.

[JDK-8364733]: https://bugs.openjdk.org/browse/JDK-8364733
[JDK-8367067]: https://bugs.openjdk.org/browse/JDK-8367067

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Commit messages:
 - Document exception wrapping in `HttpClientImpl::send`
 - Fix test failures
 - Ensure `sendAsync` wraps execution failures in `IOException`

Changes: https://git.openjdk.org/jdk/pull/27787/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27787&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368249
  Stats: 379 lines in 7 files changed: 323 ins; 41 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/27787.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27787/head:pull/27787

PR: https://git.openjdk.org/jdk/pull/27787