RFR: 8326949: Authorization header is removed when a proxy Authenticator is set on HttpClient [v2]

[Michael McMahon]

> This fix relaxes the constraints on user set authentication headers. Currently, any user set authentication headers are filtered out, if the HttpClient has an Authenticator set. The reason being that the authenticator is expected to manage authentication.  With this fix, it will be possible to use pre-emptive authentication through user set headers, even if an authenticator is set. The expected use case is where the authenticator would manage either proxy or server authentication and the user set headers would manage server authentication if the authenticator is managing proxy (or vice versa).
> If the pre-emptive authentication fails, then this behavior is disabled on further retries and it would be up to the authenticator to provide the right credentials then.
> 
> Thanks,
> Michael

Michael McMahon has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 10 additional commits since the last revision:

 - update
 - implementation rework
 - Merge branch 'master' into 8326949-authorize
 - test update
 - test update
 - test update
 - test update
 - initial impl with test
 - Merge branch 'master' into 8326949-authorize
 - impl for fix

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Changes:
  - all: https://git.openjdk.org/jdk/pull/21249/files
  - new: https://git.openjdk.org/jdk/pull/21249/files/fab3a25e..1e8b42b6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21249&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21249&range=00-01

  Stats: 27600 lines in 593 files changed: 20666 ins; 4015 del; 2919 mod
  Patch: https://git.openjdk.org/jdk/pull/21249.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21249/head:pull/21249

PR: https://git.openjdk.org/jdk/pull/21249