RFR: 8315968: Consolidate java.util.Digits and StringLatin1::PACKED_DIGITS [v6]

[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 updated the pull request incrementally with two additional commits since the last revision:

 - remove duplicate stringSize
 - update related comments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15651/files
  - new: https://git.openjdk.org/jdk/pull/15651/files/0586c64f..ebcecc34

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15651&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15651&range=04-05

  Stats: 15 lines in 2 files changed: 2 ins; 11 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