RFR: 8339699: Optimize DataOutputStream writeUTF

[Shaojin Wen]

PR #20772 introduced an optimization for writeUTF, which can also be used in DataOutputStream::writeUTF.

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Commit messages:
 - extract to JDKUTF
 - code style
 - optimize ObjectOutputStream#writeUTF
 - optimize DataOutputStream#writeUTF
 - add benchmark

Changes: https://git.openjdk.org/jdk/pull/20886/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20886&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339699
  Stats: 393 lines in 5 files changed: 212 ins; 151 del; 30 mod
  Patch: https://git.openjdk.org/jdk/pull/20886.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20886/head:pull/20886

PR: https://git.openjdk.org/jdk/pull/20886