RFR: 8357708: com.sun.jndi.ldap.Connection ignores queued LDAP replies if Connection is subsequently closed

[Jaikiran Pai]

Can I please get a review of this change which proposes to address the issue noted in https://bugs.openjdk.org/browse/JDK-8357708?

As noted in the issue, the current code in `com.sun.jndi.ldap.Connection.readReply()` is susceptible to throwing a `ServiceUnavailableException` even when the LDAP replies have already been received and queued for processing. The JBS issue has additional details about how that can happen.

The commit in this PR simplifies the code in `com.sun.jndi.ldap.LdapRequest` to make sure it always gives out the replies that have been queued when the `LdapRequest.getReplyBer()` gets invoked. One of those queued values could be markers for a cancelled or closed request. In that case, the `getReplyBer()`, like previously, continues to throw the right exception. With this change, the call to `replies.take()` or `replies.poll()` (with an infinite timeout) is no longer expected to hang forever, if the `Connection` is closed (or the request cancelled). This then allows us to remove the connection closure (`sock == null`) check in `Connection.readReply()`.

A new jtreg test has been introduced to reproduce this issue and verify the fix. The test reproduces this issue consistently when the source fix isn't present. With the fix present, even after several thousand runs of this test, the issue no longer reproduces.

tier1, tier2 and tier3 tests continue to pass with this change. I've marked the fix version of this issue for 26 and I don't plan to push this for 25.

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Commit messages:
 - add test
 - 8357708: com.sun.jndi.ldap.Connection ignores queued LDAP replies if Connection is subsequently closed

Changes: https://git.openjdk.org/jdk/pull/25449/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25449&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357708
  Stats: 533 lines in 3 files changed: 440 ins; 58 del; 35 mod
  Patch: https://git.openjdk.org/jdk/pull/25449.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25449/head:pull/25449

PR: https://git.openjdk.org/jdk/pull/25449