[Enhanced Switch][Regression] Incorrect duplicate case error since https://github.com/eclipse-jdt/eclipse.jdt.core/pull/3264

[srikanth-sankaran]

Found by code inspection and white box testing:

#3264 has introduced a bug due to which on master we incorrectly report Duplicate case in some situations such as below:

public class X {
	public static void main(String[] args) {
		Integer i = 42;
		switch (i) {
			case 2 -> System.out.println(1);
			case Integer ii when ii == 13 -> System.out.println("13");
			case 13 -> System.out.println();
			case 14 -> System.out.println();
			default -> System.out.println("Default");
		}
	}
}

Basically, we need a pattern sandwiched between constants for the problem to show up.

Fortunately PR #3310 already addresses that. I will add a regression test from here