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

[温绍锦]

On Tue, 19 Sep 2023 16:15:12 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

> 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.

Changes related to FormatItem have been reverted because too many changes were made. The duplicate code of getChars and digits will be solved with another PR later.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/15699#issuecomment-1741703218