RFR: 8349135: Add tests for HttpRequest.Builder.copy() [v5]

[Volkan Yazici]

> Adds `HttpRequest.Builder::copy` tests to `HttpRequestBuilderTest`.

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

  Fix `assertEquals()` argument order

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Changes:
  - all: https://git.openjdk.org/jdk/pull/23415/files
  - new: https://git.openjdk.org/jdk/pull/23415/files/5eddbf7d..9f7b054b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23415&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23415&range=03-04

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/23415.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23415/head:pull/23415

PR: https://git.openjdk.org/jdk/pull/23415