RFR: 8208693: HttpClient: Extend the request timeout's scope to cover the response body [v8]

[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 31 commits:

 - Shorten `TimeoutResponseTestSupport` using imports
 - Make `MultiExchange::cancelTimer` package-private
 - Merge remote-tracking branch 'upstream/master' into respBodyTime
 - Simplify Javadoc
 - Merge remote-tracking branch 'upstream/master' into respBodyTime
 - Improve `HttpBodySubscriberWrapper::onTermination` JavaDoc
 - Mark `SubscriptionWrapper` as `final`
 - Replace wrapper's `preTerminationCallback` argument with a method to be extended
 - Fix `HttpClient` doc typo
 - Invoke `preTerminationCallback` at `cancel()` too
 - ... and 21 more: https://git.openjdk.org/jdk/compare/ef464d69...55396846

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Changes: https://git.openjdk.org/jdk/pull/27469/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27469&range=07
  Stats: 840 lines in 12 files changed: 829 ins; 5 del; 6 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