Migrate boxWithJava tests to multi-file framework

compiler/testData/codegen/boxWithJava/builtinStubMethods/extendJavaCollections.kt

@@ -0,0 +1,28 @@
+// FILE: Test.java
+
+import java.lang.*;
+import java.util.*;
+
+public class Test {
+    public static class MapEntryImpl implements Map.Entry<String, String> {
+        public String getKey() { return null; }
+        public String getValue() { return null; }
+        public String setValue(String s) { return null; }
+    }
+}
+
+// FILE: main.kt
+
+//class MyIterable : Test.IterableImpl()
+//class MyIterator : Test.IteratorImpl()
+class MyMapEntry : Test.MapEntryImpl()
+
+fun box(): String {
+
+    val b = MyMapEntry()
+    b.key
+    b.value
+    b.setValue(null)
+
+    return "OK"
+}