RFR: 8369595: HttpClient: HttpHeaders.firstValueAsLong failures should be converted to ProtocolException [v2]

[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:

  Address review remarks

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/28431/files
  - new: https://git.openjdk.org/jdk/pull/28431/files/700d6d4b..b491c9bc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28431&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28431&range=00-01

  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 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