JEP 504 – Remove the Applet API

The current implementation is in [JEP 398](https://github.com/AloisSeckar/demos-java/blob/master/src/main/java/org/javademos/java17/jep398/DeprecateAppletApiForRemovalDemo.java).

The most recent implementation https://openjdk.org/jeps/504 need new JEP 504 demo implementation and JEP 398 should be turned into a [linking class](https://github.com/AloisSeckar/demos-java/blob/master/src/main/java/org/javademos/java21/jep446/ScopedValuesDemo.java) pointing to JEP 504.

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**NOTE:** This is an **ADVANCED** task to help with. Be sure you understand the requirements. Check previous contributions with `advanced` label and ask if you have any questions or doubts before doing work that will not be helpful.