RFR: 8208693: HttpClient: Extend the request timeout's scope to cover the response body [v12]

[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 incrementally with one additional commit since the last revision:

  Cancel timer right away if response body is not permitted

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27469/files
  - new: https://git.openjdk.org/jdk/pull/27469/files/c3210d88..4b4a8e6e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27469&range=11
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27469&range=10-11

  Stats: 8 lines in 1 file changed: 2 ins; 4 del; 2 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