`ArraysSupport::mismatch` is used by `StringLatin1::compareTo`. For `compareTo` to return the lexicographical distance between two string byte arrays, `ArraysSupport::mismatch` should guarantee that, in case of a mismatch, the smallest index is returned. Yet this is not specified by `ArraysSupport::mismatch`. Verify and document this.

This issue is found by [~rgiulietti]: https://github.com/openjdk/jdk/pull/28832/changes#r2804047503

### Demonstration

Consider inputs `ad` and `bc`. If `mismatch("ad", "bc")` returns 1 (instead of 0, which is the smallest index of the mismatch), `compareTo("ad", "bc")` will incorrectly conclude that `"ad" > "bc"` since the characters at index 1 yield `d > c`.