Migrate boxWithJava tests to multi-file framework

compiler/testData/codegen/boxWithJava/enhancedPrimitives.kt

@@ -0,0 +1,13 @@
+// FILE: J.java
+
+public class J {
+    // This test checks that although type '@org.jetbrains.annotations.NotNull Integer' is perceived as simple Int,
+    // it's correctly mapped to 'Lj.l.Integer' by JVM backend
+    public static String test(@org.jetbrains.annotations.NotNull Integer x) {
+        return "OK";
+    }
+}
+
+// FILE: box.kt
+
+fun box() = J.test(1)