RFR: 8219203: Use StringBuilder instead of StringBuffer in com.sun.jndi.dns.ResourceRecord

[Jaikiran Pai]

Can I please get a review of this change which replaces the usage of `StringBuffer` with `StringBuilder` in the methods of `com.sun.jndi.dns.ResourceRecord`? This addresses https://bugs.openjdk.org/browse/JDK-8219203.

Given the nature of the change, no new tests have been introduced.

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Commit messages:
 - 8219203: Use Unsynchronized StringBuilder in com.sun.jndi.dns.ResourceRecord.java

Changes: https://git.openjdk.org/jdk/pull/29652/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29652&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8219203
  Stats: 8 lines in 1 file changed: 0 ins; 1 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/29652.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29652/head:pull/29652

PR: https://git.openjdk.org/jdk/pull/29652