Add some new tests on functions and extension functions

compiler/testData/codegen/boxWithJava/reflection/functionReferenceErasedToKFunction/J.java

@@ -0,0 +1,10 @@
+import kotlin.jvm.functions.Function2;
+import kotlin.reflect.KMemberFunction;
+
+public class J {
+    public static String go() {
+        KMemberFunction<K, String> fun = K.Companion.getRef();
+        Object result = ((Function2) fun).invoke(new K(), "KO");
+        return (String) result;
+    }
+}