JS -- Add listener for sandbox events only if there are some actions

* When no actions then set it to null instead of empty object
* Even if a field has no actions, it needs to listen to events from the sandbox in order to be updated if an action changes something in it.

src/core/document.js

@@ -1020,6 +1020,21 @@ class PDFDocument {
     );
   }
 
+  get hasJSActions() {
+    return shadow(
+      this,
+      "hasJSActions",
+      this.fieldObjects.then(fieldObjects => {
+        return (
+          fieldObjects !== null &&
+          Object.values(fieldObjects).some(fieldObject =>
+            fieldObject.some(object => object.actions !== null)
+          )
+        );
+      })
+    );
+  }
+
   get calculationOrderIds() {
     const acroForm = this.catalog.acroForm;
     if (!acroForm || !acroForm.has("CO")) {