RFR: 8373796: Refactor java/net/httpclient/ThrowingPublishers*.java tests to use JUnit5

Tue Dec 16 13:33:04 UTC 2025

These test used to use the testng `IContextTest` API to stop tests after the first failure.
@sormuras suggested an even more elegant way to do that with JUnit.
Usage of IContextTest has been replaced with a `TestWatcher` that records the first failure and uses `Assumptions` to prevent further test execution. 

The rest of the changes were (almost) mechanical.

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Commit messages:
 - 8373796: Refactor java/net/httpclient/ThrowingPublishers*.java tests to use JUnit5

Changes: https://git.openjdk.org/jdk/pull/28846/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28846&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373796
  Stats: 192 lines in 9 files changed: 55 ins; 60 del; 77 mod
  Patch: https://git.openjdk.org/jdk/pull/28846.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28846/head:pull/28846

PR: https://git.openjdk.org/jdk/pull/28846