RFR: 8365832: Optimize FloatingDecimal and DigitList with byte[] and cleanup [v7]

[Chen Liang]

On Thu, 21 Aug 2025 16:34:52 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> Since FloatToDecimal and DoubleToDecimal are used in Float.toString and Double.toString, some code in FloatingDecimal is not used. 
>> 
>> This PR refactors `FloatingDecimal` and `DigitList` to improve efficiency and reduce code duplication.
>> 
>> Key changes:
>> * Convert internal digit storage from `char[]` to `byte[]` for reduced memory footprint.
>> *   Remove unused code and methods that are no longer needed.
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   BinaryToASCIIBuffer#getChars add javadoc

Marked as reviewed by liach (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/23311#pullrequestreview-3141677481