Add Java 20 class with new format ... (#20)

- samples for standard features
- class with markdown javadoc with JEPs

Author: mperor

src/test/java/pl/mperor/lab/java/Java20.java

@@ -0,0 +1,15 @@
+package pl.mperor.lab.java;
+
+/// Java 20™ (March 2023)
+/// [JDK 20](https://openjdk.org/projects/jdk/20)
+///
+/// - PREVIEW & INCUBATOR:
+///     - 429:	Scoped Values (Incubator)
+///     - 432:	Record Patterns (Second Preview)
+///     - 433:	Pattern Matching for switch (Fourth Preview)
+///     - 434:	Foreign Function & Memory API (Second Preview)
+///     - 436:	Virtual Threads (Second Preview)
+///     - 437:	Structured Concurrency (Second Incubator)
+///     - 438:	Vector API (Fifth Incubator)
+public class Java20 {
+}