Migrate boxAgainstJava tests to multi-file framework

compiler/testData/codegen/boxAgainstJava/sam/adapters/nonLiteralNull.kt

@@ -1,4 +1,14 @@
+// FILE: JavaClass.java
+
+class JavaClass {
+    public static String run(Runnable r) {
+        return r == null ? "OK" : "FAIL";
+    }
+}
+
+// FILE: 1.kt
+
 fun box(): String {
     val f: (() -> Unit)? = null
     return JavaClass.run(f)!!
-}
+}