[jdk17u-dev] RFR: 8294916: Cancelling a request must eventually cause its response body subscriber to be unregistered

[Goetz Lindenmaier]

I backport this for parity with 17.0.17-oracle.

the change itself applied clean.  The tests needed some 
changes to work:

test/jdk/java/net/httpclient/CancelStreamedBodyTest.java
A new test that lacks the changes of later change JDK-8295944
that was already backported.

test/jdk/java/net/httpclient/SmallTimeout.java
The test calls close() of ExecutorService which is a method
introduced after jdk17.  I implemented the functionality 
locally in the test.

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

Commit messages:
 - Work around missing executor.close()
 - Parts of 8295944
 - Backport dcd46501e6a25ac875d61bfbd412555b933ce34c

Changes: https://git.openjdk.org/jdk17u-dev/pull/3669/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=3669&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294916
  Stats: 666 lines in 9 files changed: 641 ins; 1 del; 24 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/3669.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/3669/head:pull/3669

PR: https://git.openjdk.org/jdk17u-dev/pull/3669