RFR: 8337167: StringSize deduplication

[Shaojin Wen]

Integer.stringSize and Long.stringSize are used not only in java.lang, but also in other places. We put stringSize in DecimalDigits to reduce duplicate code and the use of JLA.

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Commit messages:
 - stringSize deduplication

Changes: https://git.openjdk.org/jdk/pull/20322/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20322&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337167
  Stats: 99 lines in 8 files changed: 32 ins; 57 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/20322.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20322/head:pull/20322

PR: https://git.openjdk.org/jdk/pull/20322