RFR: 8300011: Refactor code examples to use @snippet in java.util.TimeZone

[Justin Lu]

This PR implements JEP 413: Code Snippets in Java API Documentation for _[java.util.TimeZone](https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/util/TimeZone.html)_.

Code examples using <pre> ...  </pre> blocks are replaced with the @ snippet syntax where applicable.

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Commit messages:
 - Replace <pre> blocks with @snippet

Changes: https://git.openjdk.org/jdk/pull/11955/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11955&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300011
  Stats: 13 lines in 1 file changed: 0 ins; 0 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/11955.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11955/head:pull/11955

PR: https://git.openjdk.org/jdk/pull/11955