RFR: 8349135: Add tests for HttpRequest.Builder.copy() [v3]

[Volkan Yazici]

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

Volkan Yazici 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 three additional commits since the last revision:

 - Merge remote-tracking branch 'upstream/master' into HttpRequest-Builder-copy-Test
 - Update copyright year
 - Verify `copy()` in `HttpRequestBuilderTest`

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/23415/files
  - new: https://git.openjdk.org/jdk/pull/23415/files/9606b4ee..4e3b9a67

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23415&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23415&range=01-02

  Stats: 536 lines in 25 files changed: 233 ins; 131 del; 172 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