[jdk21u-dev] RFR: 8365086: CookieStore.getURIs() and get(URI) should return an immutable List

[Goetz Lindenmaier]

I backport this for parity with 21.0.10-oracle.

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Commit messages:
 - Backport 022e29a77533aacabd56820d00ecffa9646a8362

Changes: https://git.openjdk.org/jdk21u-dev/pull/2369/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2369&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8365086
  Stats: 127 lines in 2 files changed: 119 ins; 4 del; 4 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2369.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2369/head:pull/2369

PR: https://git.openjdk.org/jdk21u-dev/pull/2369