RFR: 8300093: Refactor code examples to use @snippet in java.text.MessageFormat

[Iris Clark]

On Fri, 13 Jan 2023 21:47:40 GMT, Justin Lu <jlu at openjdk.org> wrote:

> This PR implements _JEP 413: Code Snippets in Java API Documentation_ for [java.text.MessageFormat](https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/text/class-use/MessageFormat.html).
> 
> Code examples using <pre> ... </pre> blocks are replaced with the @ snippet syntax where applicable.

Marked as reviewed by iris (Reviewer).

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PR: https://git.openjdk.org/jdk/pull/12001