RFR: 8316580: HttpClient with StructuredTaskScope does not close when a task fails [v2]

[Daniel Fuchs]

> Hi, 
> 
> Please find below a fix for 8316580: HttpClient with StructuredTaskScope does not close when a task fails.
> 
> The problem here is a subtle reference release issue: Interrupting the VirtualThread means that the CompletableFuture returned by sendAsync is eligible for GC after having been cancelled, which in turn means that some of the intermediate operations that would have been completed before that CF was completed get eligible for being GC’ed too. One of these intermediate operations is the action that decrements the ref counting. Since the refcount isn’t decremented properly, the client won’t exit. 
> 
> Holding onto the CompletableFuture returned to the caller by HttpClient::sendAsync until that CompletableFuture gets completed from upstream fixes the issue.

Daniel Fuchs has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into HttpGetWithCancelledStructuredScope-8316580
 - 8316580

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15883/files
  - new: https://git.openjdk.org/jdk/pull/15883/files/49644147..7e4b6a9e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15883&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15883&range=00-01

  Stats: 25605 lines in 503 files changed: 12952 ins; 10249 del; 2404 mod
  Patch: https://git.openjdk.org/jdk/pull/15883.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15883/head:pull/15883

PR: https://git.openjdk.org/jdk/pull/15883