[REF] web: x2manyField: ensure we don't pass the props viewMode if not set

Before this commit, we passed the viewMode props to the X2many field everytime.
Since that props is optional, we don't have to pass it if it is not a string (null or undefined)

This allows to display a field set as invisible in studio

Part-of: odoo/odoo#115799

addons/web/static/src/views/fields/x2many/x2many_field.js

@@ -43,7 +43,7 @@ export class X2ManyField extends Component {
             this.isMany2Many
         );
 
-        this.archInfo = this.props.views[this.props.viewMode] || {};
+        this.archInfo = this.props.views?.[this.props.viewMode] || {};
 
         const { activeActions, creates } = this.archInfo;
         if (this.props.viewMode === "kanban") {
@@ -277,11 +277,13 @@ export const x2ManyField = {
             addLabel: attrs["add-label"],
             context: dynamicInfo.context,
             domain: dynamicInfo.domain,
-            viewMode,
-            views,
             crudOptions: options,
             string,
         };
+        if (viewMode) {
+            props.views = views;
+            props.viewMode = viewMode;
+        }
         if (widget) {
             props.widget = widget;
         }