Migrate boxAgainstJava tests to multi-file framework

compiler/testData/codegen/boxAgainstJava/visibility/protectedStatic/simpleFun.kt

@@ -1,9 +1,19 @@
-class Derived(): simpleFun() {
+// FILE: Base.java
+
+public class Base {
+    protected static String protectedFun() {
+        return "OK";
+    }
+}
+
+// FILE: 1.kt
+
+class Derived : Base() {
     fun test(): String {
-        return simpleFun.protectedFun()!!
+        return Base.protectedFun()!!
     }
 }
 
 fun box(): String {
-   return Derived().test()
+    return Derived().test()
 }