RFR: 8354276: Strict HTTP header validation [v3]

[Daniel Jeliński]

> RFC 9113 HTTP/2 mandates certain validation for HTTP headers; the HttpClient don't fully implement the described requirements.
> 
> This PR adds the following validation:
> - pseudo-headers defined for requests are rejected in responses and push streams
> - pseudo-headers defined for responses are rejected in push promises
> - connection headers are rejected in responses and push streams
> 
> Connection headers are still accepted in push promises; that's because some popular server implementations were found to echo the request headers in push promises, and when the original request was a HTTP/1 upgrade, the push promise could contain one or more headers that were prohibited in HTTP/2 but allowed in HTTP/1.
> 
> An existing test was adapted to verify the handling of response headers. The modified test passes with this the changes in this PR, fails without them. Other tier1-3 tests continue to pass.

Daniel Jeliński has updated the pull request incrementally with one additional commit since the last revision:

  Add suggested comment to PSEUDO_HEADERS
  
  Co-authored-by: Michael McMahon <70538289+Michael-Mc-Mahon at users.noreply.github.com>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/24569/files
  - new: https://git.openjdk.org/jdk/pull/24569/files/c7b28290..9c945cc1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24569&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24569&range=01-02

  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/24569.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24569/head:pull/24569

PR: https://git.openjdk.org/jdk/pull/24569