Use the clone helper instead of a interal function

tp-form.js

@@ -5,6 +5,7 @@ This program is available under Apache License Version 2.0
 */
 
 import { LitElement, html, css } from 'lit';
+import { clone } from '@tp/helpers/clone.js';
 
 class TpForm extends LitElement {
   static get styles() {
@@ -373,27 +374,7 @@ class TpForm extends LitElement {
       value = control.defaultValue || control.getAttribute('default-value');
     }
 
-    let copy;
-    switch (typeof value) {
-      case 'string':
-      case 'number':
-      case 'boolean':
-        copy = value;
-        break;
-      case 'object':
-        if (Array.isArray(value)) {
-          copy = value.slice(0);
-        } else if (value === null) {
-          copy = null;
-        } else if (value instanceof Date) {
-          copy = new Date(value.getTime());
-        } else {
-          copy = Object.assign({}, value);
-        }
-        break;
-    }
-
-    return copy;
+    return clone(value);
   }
 
   _readonlyChanged() {