RFR: 8338409: Use record to simplify code

[duke]

On Fri, 2 Aug 2024 16:14:41 GMT, Shaojin Wen <duke at openjdk.org> wrote:

> j.u.Formatter$FixedString can be refactored to simplify the code using Record

@wenshao 
Your change (at version c7ce3c724183ad3b4a09a95555fac1d7411fdd8e) is now ready to be sponsored by a Committer.

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PR Comment: https://git.openjdk.org/jdk/pull/20443#issuecomment-2292421421