RFR: 8315968: Consolidate java.util.Digits and StringLatin1::PACKED_DIGITS

[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

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Commit messages:
 - reduce duplicate

Changes: https://git.openjdk.org/jdk/pull/15651/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15651&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315968
  Stats: 114 lines in 3 files changed: 73 ins; 33 del; 8 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