RFR: 8208693: HttpClient: Extend the request timeout's scope to cover the response body [v16]

[Volkan Yazici]

> Currently `HttpRequest::timeout` only applies until the response headers are received. Extend its scope to also cover the consumption of the response body.
> 
> ### Review guidelines
> 
> 1. Read _"the fix"_ in `MultiExchange`
> 2. Skim through the test server *handler* in `TimeoutResponseTestSupport`
> 3. Review first `TimeoutResponseHeaderTest`, and then `TimeoutResponseBodyTest` (Mind the multiple `@test` blocks!)

Volkan Yazici has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 42 commits:

 - Merge remote-tracking branch 'upstream/master' into respBodyTime
 - Update JavaDocs to match the spec
 - Move `cancelTimerOnResponseBodySubscriberTermination` to `ExchangeImpl`
 - Exclude disallowed timer cancellations
 - Merge remote-tracking branch 'upstream/master' into respBodyTime
 - Cancel timer right away if response body is not permitted
 - Configure timeout for the `WebSocketTest`
 - Use `var`
 - Clarify WebSocket behaviour and test it
 - Verify no lingering response timers
 - ... and 32 more: https://git.openjdk.org/jdk/compare/7278d2e8...5f99578a

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Changes: https://git.openjdk.org/jdk/pull/27469/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27469&range=15
  Stats: 1093 lines in 15 files changed: 1068 ins; 5 del; 20 mod
  Patch: https://git.openjdk.org/jdk/pull/27469.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27469/head:pull/27469

PR: https://git.openjdk.org/jdk/pull/27469