RFR: 8367976: Validate and clamp jdk.httpclient.bufsize [v5]

[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?

Volkan Yazici has updated the pull request incrementally with one additional commit since the last revision:

  Use `HttpTestEchoHandler` and improve styling

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27874/files
  - new: https://git.openjdk.org/jdk/pull/27874/files/26fdcb4a..92f07382

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27874&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27874&range=03-04

  Stats: 29 lines in 1 file changed: 6 ins; 19 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