RFR: 8316150: Refactor get chars and string size [v21]

[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:

  restore StringUTF16.getChars(int,int,int,byte[]) and StringUTF16.getChars(long,int,int,byte[])

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15699/files
  - new: https://git.openjdk.org/jdk/pull/15699/files/ebbb5597..8ec66cca

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15699&range=20
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15699&range=19-20

  Stats: 14 lines in 1 file changed: 14 ins; 0 del; 0 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