[jdk11u] RFR: 8296410: HttpClient throws java.io.IOException: no statuscode in response for HTTP2

[Alexey Bakhtin]

Please review the backport of JDK-8296410 to 11u

Stream.java is applied cleanly.

BodyOutputStream.java, Http2TestServer.java, and Http2TestServerConnection.java test library classes are in another path and the package name. They are applied cleanly after updating the path to the files.

New TrailingHeadersTest is updated:

fixed reference to the Http2TestServer module
fixed instanceOf pattern issue
Added Http2TestServerConnection::addToOutputQ method required for the test functionality

All java/net/httpclient JTREG tests passed

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Commit messages:
 - Backport f4b140b4200fc0f49161395501d3dbcba7a79059

Changes: https://git.openjdk.org/jdk11u/pull/96/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk11u&pr=96&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296410
  Stats: 434 lines in 5 files changed: 392 ins; 14 del; 28 mod
  Patch: https://git.openjdk.org/jdk11u/pull/96.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u.git pull/96/head:pull/96

PR: https://git.openjdk.org/jdk11u/pull/96