[code-reflection] Integrated: Pass comparator to TreeSet

[Paul Sandoz]

Fix auto diff test after `Value` was updated to no longer implement `Comparable`

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Commit messages:
 - Pass comparator to TreeSet

Changes: https://git.openjdk.org/babylon/pull/862/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=862&range=00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/babylon/pull/862.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/862/head:pull/862

PR: https://git.openjdk.org/babylon/pull/862