RFR: 8336278: Micro-optimize Replace String.format("%n") to System.lineSeparator

[Shaojin Wen]

There are three places in the JDK code where String.format("%n") is used. This is actually equivalent to System.lineSeparator and does not require the implementation of String.format.

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Commit messages:
 - replace String.format("%n") to System.lineSeparator()

Changes: https://git.openjdk.org/jdk/pull/20149/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20149&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336278
  Stats: 6 lines in 3 files changed: 0 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/20149.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20149/head:pull/20149

PR: https://git.openjdk.org/jdk/pull/20149