RFR: 8377796: java.net.http.HttpClient.send() and sendAsync() never complete when BodyHandler.apply() returns null [v3]

[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-8377796?
> 
> The change here asserts that if `BodyHandler.apply()` returns `null`, then the HTTP request completes exceptionally. A new test has been introduced to reproduce the issue and verify the fix.

Jaikiran Pai has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains seven commits:

 - Daniel's suggestion - assert warmup is only for HTTP/2
 - merge latest from master branch
 - split the test method arguments into individual parts
 - no need for the duplicate null check
 - use HttpTestEchoHandler in the new test
 - add a test
 - 8377796: java.net.http.HttpClient.send() and sendAsync() never complete when BodyHandler.apply() returns null

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Changes: https://git.openjdk.org/jdk/pull/29691/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29691&range=02
  Stats: 326 lines in 5 files changed: 252 ins; 9 del; 65 mod
  Patch: https://git.openjdk.org/jdk/pull/29691.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29691/head:pull/29691

PR: https://git.openjdk.org/jdk/pull/29691