RFR: 8315968: Consolidate java.util.Digits and StringLatin1::PACKED_DIGITS [v15]

[温绍锦]

> Some codes in core libs are duplicated, including:
> java.util.DecimalDigits::DIGITS -> java.lang.StringLatin1.PACKED_DIGITS
> java.util.DecimalDigits::size -> java.lang.Long.stringSize
> 
> We can reduce duplication through JavaLangAccess, which is also needed in other places, such as:
> https://github.com/openjdk/jdk/pull/15555

温绍锦 has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains two new commits since the last revision:

 - use StringLatin1.PACKED_DIGITS and add getCharsLatin1
 - rebase & resolve DecimalDigits delete and add

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15651/files
  - new: https://git.openjdk.org/jdk/pull/15651/files/6cc34bed..70bf2297

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15651&range=14
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15651&range=13-14

  Stats: 6 lines in 1 file changed: 4 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/15651.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15651/head:pull/15651

PR: https://git.openjdk.org/jdk/pull/15651