Migrate boxAgainstJava tests to multi-file framework

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

@@ -1,3 +1,15 @@
-fun box(): String {
-    return unrelatedUpperBounds.id("OK" as java.lang.String)!! as kotlin.String
+// FILE: Foo.java
+
+import java.util.Collection;
+
+public class Foo {
+    public static <T extends CharSequence & java.io.Serializable> T id(T p) {
+        return p;
+    }
+}
+
+// FILE: 1.kt
+
+fun box(): String {
+    return Foo.id("OK" as java.lang.String)!! as kotlin.String
 }