RFR: 8357685: Changing the type of Integer::digits from char[] to byte[]

[Shaojin Wen]

Integer::digits type can use byte[] instead of char[], which can reduce the conversion from char to byte in the process of Integer.toString. Using byte[] can also save memory.

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Commit messages:
 - char[] -> byte[]

Changes: https://git.openjdk.org/jdk/pull/25426/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25426&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357685
  Stats: 7 lines in 2 files changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/25426.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25426/head:pull/25426

PR: https://git.openjdk.org/jdk/pull/25426