Modernise form components (#5923)

Co-authored-by: Tim Jacomb <21194782+timja@users.noreply.github.com>
Co-authored-by: Tim Jacomb <timjacomb1+github@gmail.com>

core/src/main/java/hudson/Functions.java

@@ -2289,4 +2289,10 @@ public class Functions {
             return true;
         }
     }
+
+    @SuppressFBWarnings(value = "PREDICTABLE_RANDOM", justification = "True randomness isn't necessary for form item IDs")
+    @Restricted(NoExternalUse.class)
+    public static String generateItemId() {
+        return String.valueOf(Math.floor(Math.random() * 3000));
+    }
 }