RFR: 8342650: Move getChars to DecimalDigits [v2]

[Shaojin Wen]

> Move getChars methods of StringLatin1 and StringUTF16 to DecimalDigits to reduce duplication
> 
> 1. HexDigits and OctalDigits also include getCharsLatin1 and getCharsUTF16
> 2. Putting these two methods into DecimalDigits can avoid the need to expose them in JavaLangAccess
> 3. Eliminate duplicate code in BigDecimal

Shaojin Wen has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 11 additional commits since the last revision:

 - Merge remote-tracking branch 'upstream/master' into int_get_chars_dedup_202410
 - fix Helper
 - fix Helper
 - fix Helper
 - unsafe putByte
 - remove digitPair
 - fix import
 - remove JLA
 - remove unused code
 - add comments
 - ... and 1 more: https://git.openjdk.org/jdk/compare/b209cf90...73b32004

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21593/files
  - new: https://git.openjdk.org/jdk/pull/21593/files/65dbe676..73b32004

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21593&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21593&range=00-01

  Stats: 215050 lines in 1978 files changed: 123180 ins; 69459 del; 22411 mod
  Patch: https://git.openjdk.org/jdk/pull/21593.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21593/head:pull/21593

PR: https://git.openjdk.org/jdk/pull/21593