RFR: 8377903: ArraysSupport::mismatch should document that they return the smallest index

[Raffaello Giulietti]

A doc only change to clarify that the _smallest_ of many possible mismatch indices is returned.

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Commit messages:
 - 8377903: ArraysSupport::mismatch should document that they return the smallest index.

Changes: https://git.openjdk.org/jdk/pull/29997/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29997&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8377903
  Stats: 7 lines in 1 file changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/29997.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29997/head:pull/29997

PR: https://git.openjdk.org/jdk/pull/29997