RFR: 8316150: Refactor get chars and string size [v5]

[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 with a new target base due to a merge or a rebase. The pull request now contains eight commits:

 - rebase from master & refactor digits
 - rebase from master
 - Merge remote-tracking branch 'upstream/master' into refactor_get_chars_and_string_size
   
   # Conflicts:
   #	src/java.base/share/classes/java/lang/StringLatin1.java
 - add comment
 - fix build error
 - fix build error
 - move StringLatin1::getChars to jdk.internal.util.DecimalDigits::getCharsLatin1
 - move *::stringSize to jdk.internal.util.DecimalDigits::stringSize

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Changes: https://git.openjdk.org/jdk/pull/15699/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15699&range=04
  Stats: 516 lines in 12 files changed: 149 ins; 280 del; 87 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