RFR: 8316150: Refactor get chars and string size [v18]

[温绍锦]

> 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:

  refactor & bug fix

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15699/files
  - new: https://git.openjdk.org/jdk/pull/15699/files/a7c21d24..ab6377ea

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15699&range=17
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15699&range=16-17

  Stats: 25 lines in 3 files changed: 4 ins; 12 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/15699.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15699/head:pull/15699

PR: https://git.openjdk.org/jdk/pull/15699