RFR: 8339699: Optimize DataOutputStream writeUTF [v4]

[Shaojin Wen]

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

Shaojin Wen has updated the pull request incrementally with two additional commits since the last revision:

 - rename JDKUTF to ModifiedUtf
 - suggestion from @liach

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20886/files
  - new: https://git.openjdk.org/jdk/pull/20886/files/9744e8a5..58a23d4f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20886&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20886&range=02-03

  Stats: 47 lines in 4 files changed: 21 ins; 15 del; 11 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