Migrate boxAgainstJava tests to multi-file framework

compiler/testData/codegen/boxAgainstJava/functions/max.kt

@@ -1,3 +1,15 @@
-fun box(): String {
-    return max.max(java.util.Arrays.asList("AK", "OK", "EK"))!!
+// FILE: Foo.java
+
+import java.util.*;
+
+public class Foo {
+    public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) {
+        return Collections.max(coll);
+    }
+}
+
+// FILE: 1.kt
+
+fun box(): String {
+    return Foo.max(java.util.Arrays.asList("AK", "OK", "EK"))!!
 }