RFR: 8368249: HttpClient: Translate exceptions thrown by sendAsync [v6]

[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

Volkan Yazici has updated the pull request incrementally with three additional commits since the last revision:

 - Avoid peeling off `UncheckedIOException`
 - Minimize bodies passed to `assertThrows()`
 - Improve `HttpClientImpl` comments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27787/files
  - new: https://git.openjdk.org/jdk/pull/27787/files/f2fa01df..5621d911

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27787&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27787&range=04-05

  Stats: 73 lines in 2 files changed: 4 ins; 3 del; 66 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