RFR: 8335181: Incorrect handling of HTTP/2 GOAWAY frames in HttpClient

[Jaikiran Pai]

This is a fresh version of the PR that I had opened here https://github.com/openjdk/jdk/pull/20442. A `git merge` command ended up causing unexpected issues with that old PR.

The commits in this PR are the ones which were already reviewed and a new one which was done to implement Daniel's suggestion in the review. test repeat 50 of java/net/httpclient had passed without any issues for that old PR. But before integrating this PR, I will rerun all relevant tests again to be sure nothing unexpected shows up.

Sorry that this has to be reviewed afresh.

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Commit messages:
 - also decrement streams to allow the HttpClient to close
 - Daniel's suggestion - call closeAsUnprocessed() from handleReset
 - simplify request approver test construct - no need to expect request path
 - move the unprocessed state tracking to ExchangeImpl
 - reorder setFinalStream and markHalfClosedRemote
 - simplify test, handle REFUSED_STREAM on the client side, fix WindowController assertion
 - add code comment to a test class
 - 8335181: Incorrect handling of HTTP/2 GOAWAY frames in HttpClient

Changes: https://git.openjdk.org/jdk/pull/20567/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20567&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8335181
  Stats: 615 lines in 12 files changed: 560 ins; 2 del; 53 mod
  Patch: https://git.openjdk.org/jdk/pull/20567.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20567/head:pull/20567

PR: https://git.openjdk.org/jdk/pull/20567