RFR: 8316150: Refactor get chars and string size [v4]

[Roger Riggs]

On Wed, 13 Sep 2023 14:08:15 GMT, 温绍锦 <duke at openjdk.org> wrote:

>> 1. Reduce duplicate stringSize code
>> 2. Move java.lang.StringLatin1.getChars to jdk.internal.util.DecimalDigits::getCharLatin1，not only java.lang, other packages also need to use this method
>
> 温绍锦 has updated the pull request incrementally with one additional commit since the last revision:
> 
>   add comment

There's a lot of duplication exposed here between the `digits` method and the `getCharsLatin1` method that should be resolved. 
Can the callers of `getCharsLatin1` be converted to use `digits`?  

We also should keep HexDigits and OctalDigits classes have a consistent API and functionality.

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PR Comment: https://git.openjdk.org/jdk/pull/15699#issuecomment-1726019081