[lahodaj]

Consider code like this:

public class X {
    private void tt() {
        int i = switch (0) {
            default:
                yield 0;
        };
    }
}

Select the 0 in yield 0;, and try to introduce variable for it. This will crash with:

SEVERE [org.openide.util.RequestProcessor]: Error in RequestProcessor org.netbeans.modules.editor.hints.HintsUI$1
java.lang.AssertionError: Diff not implemented: YIELD com.sun.tools.javac.tree.JCTree$JCYield
        at org.netbeans.modules.java.source.save.CasualDiff.diffTreeImpl0(CasualDiff.java:5898)
        at org.netbeans.modules.java.source.save.CasualDiff.diffTreeImpl(CasualDiff.java:5570)
...

I.e. the CasualDiff is not handling yield. This PR adds handling of yield based on return (except, unlike return, yield always has a value).

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[mbien]

looks good!