Add support for running Java 21 "Unnamed classes and Instance main method" #1444

vscode-java now provides support for Java 21 preview feature Unnamed classes and Instance main method, however, we're missing the Run/Debug codelens on the main() method

Environment

• Operating System: MacOS 14.3 (23D56)
• JDK version: 21.0.1 temurin
• Visual Studio Code version: 1.86.2
• Java extension version: 1.28.1
• Java Debugger extension version: 0.56.2024020601 pre-release

Steps To Reproduce

1. Set Java 21 as the default runtime
2. Create a hello.java file
3. Paste this code:

String greeting = "Hello, World!";

void main() {
    System.out.println(greeting);
}

Current Result

No Run/Debug codelenses

Expected Result

Should be able to Run/Debug the class via codelenses either at the top of the file or over the main() method

Additional Informations