Migrate boxAgainstJava tests to multi-file framework

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

@@ -1,9 +1,22 @@
-class Derived(): simpleClass() {
+// FILE: Base.java
+
+public class Base {
+    protected static class Inner {
+        public Inner() {}
+        public String foo() {
+            return "OK";
+        }
+    }
+}
+
+// FILE: 1.kt
+
+class Derived : Base() {
     fun test(): String {
-        return simpleClass.Inner().foo()!!
+        return Base.Inner().foo()!!
     }
 }
 
 fun box(): String {
-   return Derived().test()
+    return Derived().test()
 }