RFR: 8361715: (bf) Improve java/nio/Buffer/GetChars.java and migrate to JUnit [v10]

[Roger Riggs]

On Fri, 25 Jul 2025 17:47:32 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> should I include this issue's bug (8361715), or just the actual defect which drove the desire to add some tests (8361299 - which I will copy forward from GetChars)?
>
> 8361299 and 8343110 the issues containing the bug/enhancement being tested.
> 8343110 is the enhancement that added CharSequence.getChars and 8361299 an issue fixed after the original.

Jtreg has a useful feature to run tests by bugid:
```-bug:<bugid>    Run only those tests which apply to the given bugid.```

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PR Review Comment: https://git.openjdk.org/jdk/pull/26282#discussion_r2231707310