RFR: 8326498: java.net.http.HttpClient connection leak using http/2 [v2]

[Jaikiran Pai]

> Can I please get a review for this fix which addresses a connection leak in HttpClient when dealing with HTTP/2 requests?
> 
> I have added a comment in https://bugs.openjdk.org/browse/JDK-8326498 which explains what the issue is. The fix here addresses the issue by cleaning up the `Http2Connection` closing logic and centralizing it to a connection terminator. The terminator then ensures that the right resources are closed (including the underlying SocketChannel) when the termination happens.
> 
> A new jtreg test has been introduced which reproduces the issue and verifies the fix.

Jaikiran Pai has updated the pull request incrementally with two additional commits since the last revision:

 - mark jdk.internal.net.http.Http2Connection as Closable
 - reduce number of concurrent requests

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/28233/files
  - new: https://git.openjdk.org/jdk/pull/28233/files/6c983026..3e4574b4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28233&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28233&range=00-01

  Stats: 5 lines in 2 files changed: 2 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/28233.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28233/head:pull/28233

PR: https://git.openjdk.org/jdk/pull/28233