RFR: 8316150: Refactor get chars and string size [v7]

[wickund]

On Fri, 22 Sep 2023 09:22:04 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:
> 
>   restore HexDigits & OctalDigits

Changes requested by wickund at github.com (no known OpenJDK username).

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PR Review: https://git.openjdk.org/jdk/pull/15699#pullrequestreview-1639806273