RFR: 8369595: HttpClient: HttpHeaders.firstValueAsLong failures should be converted to ProtocolException [v5]

[Volkan Yazici]

> Add guards against `HttpHeaders::firstValueAsLong` failures. `H3MalformedResponseTest` is overhauled – migrated to JUnit, reinforced with exception type tests, etc. – but not all `firstValueAsLong` changes are verified with new additional tests. `test/jdk/java/net/httpclient/` tests still do pass.

Volkan Yazici has updated the pull request incrementally with one additional commit since the last revision:

  Introduce dangling `firstValueAsLong("content-length")` calls back

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Changes:
  - all: https://git.openjdk.org/jdk/pull/28431/files
  - new: https://git.openjdk.org/jdk/pull/28431/files/d2d9adfe..0af344f1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28431&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28431&range=03-04

  Stats: 12 lines in 1 file changed: 12 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28431.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28431/head:pull/28431

PR: https://git.openjdk.org/jdk/pull/28431