Migrate boxWithJava tests to multi-file framework

compiler/testData/codegen/boxWithJava/reflection/functionReferenceErasedToKFunction.kt

@@ -0,0 +1,28 @@
+// FILE: J.java
+
+import kotlin.jvm.functions.Function2;
+import kotlin.reflect.KFunction;
+
+public class J {
+    public static String go() {
+        KFunction<String> fun = K.Companion.getRef();
+        Object result = ((Function2) fun).invoke(new K(), "KO");
+        return (String) result;
+    }
+}
+
+// FILE: K.kt
+
+class K {
+    fun reverse(s: String): String {
+        return s.reversed()
+    }
+
+    companion object {
+        fun getRef() = K::reverse
+    }
+}
+
+fun box(): String {
+    return J.go()
+}