RFR: 8339290: Optimize ClassFile Utf8EntryImpl#writeTo

[Shaojin Wen]

Use fast path for ascii characters 1 to 127 to improve the performance of writing Utf8Entry to BufferWriter.

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Commit messages:
 - bug fix
 - optimize Utf8EntryImpl#writeTo

Changes: https://git.openjdk.org/jdk/pull/20772/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20772&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339290
  Stats: 70 lines in 5 files changed: 32 ins; 1 del; 37 mod
  Patch: https://git.openjdk.org/jdk/pull/20772.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20772/head:pull/20772

PR: https://git.openjdk.org/jdk/pull/20772