RFR: 8367976: Validate and clamp jdk.httpclient.bufsize

[Volkan Yazici]

Validate and clamp the value populated from the `jdk.httpclient.bufsize` system property. Added two new tests: Does clamping work? Does the minimum value wedge the client?

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Commit messages:
 - Clamp `Utils::BUFSIZE`

Changes: https://git.openjdk.org/jdk/pull/27874/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27874&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367976
  Stats: 230 lines in 4 files changed: 216 ins; 10 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/27874.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27874/head:pull/27874

PR: https://git.openjdk.org/jdk/pull/27874