RFR: 8373808: Refactor java/net/httpclient qpack and hpack tests to use JUnit

[Aleksei Efimov]

The change below refactors QPack and HPack HttpClient tests to use the JUnit test framework instead of the TestNG one.
No failures of the modified tests seen with:
`make test TEST=open/test/jdk/java/net/httpclient/http2/Hpack*\ open/test/jdk/java/net/httpclient/qpack`

Test-framework stats after the modification:
QPack tests:
 `Framework-based tests: 2,385 = 0 TestNG + 2,385 JUnit`
HPack tests:
  `Framework-based tests: 108 = 0 TestNG + 108 JUnit`

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Commit messages:
 - fix formatting
 - Merge branch 'master' into JDK-8373808_refactor_hqpack_junit
 - 8373808: Refactor java/net/httpclient qpack and hpack tests to use JUnit

Changes: https://git.openjdk.org/jdk/pull/28900/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28900&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373808
  Stats: 497 lines in 31 files changed: 99 ins; 70 del; 328 mod
  Patch: https://git.openjdk.org/jdk/pull/28900.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28900/head:pull/28900

PR: https://git.openjdk.org/jdk/pull/28900