RFR: 8316150: Refactor get chars and string size [v16]

[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 two additional commits since the last revision:

 - remove unused throws
 - refactor from #15836

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15699/files
  - new: https://git.openjdk.org/jdk/pull/15699/files/1ab0fbd0..e1c4fdea

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15699&range=15
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15699&range=14-15

  Stats: 67 lines in 4 files changed: 20 ins; 16 del; 31 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