[jdk21u-dev] RFR: 8364263: HttpClient: Improve encapsulation of ProxyServer

[Goetz Lindenmaier]

I backport this for parity with 21.0.10-oracle.

Resolved one chunk, run() looks quite different. 
Mitght be clean anyways.

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Commit messages:
 - backport 190e113031bc6ece781fdf0d9f3c853ce324f170

Changes: https://git.openjdk.org/jdk21u-dev/pull/2340/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2340&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8364263
  Stats: 20 lines in 1 file changed: 2 ins; 10 del; 8 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2340.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2340/head:pull/2340

PR: https://git.openjdk.org/jdk21u-dev/pull/2340