[OpenJDK 2D-Dev] RFR: 8264428: Replace uses of StringBuffer with StringBuilder in java.desktop

[Andrey Turbanov]

Found by IntelliJ IDEA inspection `Java | Java language level migration aids | Java 5 | 'StringBuffer' may be 'StringBuilder'`
As suggested in https://github.com/openjdk/jdk/pull/1507#issuecomment-757369003 I've created separate PR for module `java.desktop`
Similar cleanups in the past: https://bugs.openjdk.java.net/browse/JDK-8041679 https://bugs.openjdk.java.net/browse/JDK-8264029

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Commit messages:
 - [PATCH] Replace uses of StringBuffer with StringBuilder in java.desktop

Changes: https://git.openjdk.java.net/jdk/pull/3251/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3251&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264428
  Stats: 44 lines in 11 files changed: 0 ins; 8 del; 36 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3251.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3251/head:pull/3251

PR: https://git.openjdk.java.net/jdk/pull/3251