RFR: 8291598: Matcher.appendReplacement should not create new StringBuilder instances

[Raffaello Giulietti]

Remove instantiation of `StringBuilder`

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Commit messages:
 - 8291598: Matcher.appendReplacement should not create new StringBuilder instances

Changes: https://git.openjdk.org/jdk/pull/13048/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13048&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291598
  Stats: 152 lines in 1 file changed: 62 ins; 52 del; 38 mod
  Patch: https://git.openjdk.org/jdk/pull/13048.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/13048/head:pull/13048

PR: https://git.openjdk.org/jdk/pull/13048