Add IBaseWidget.serialize flag (#915)

https://github.com/Comfy-Org/ComfyUI_frontend/pull/3323

Some widgets are only used for display purpose (The preview image
widget), their value shouldn't be serialized into the workflow. This PR
adds a flag to allow widget to skip value serialization.

src/LGraphNode.ts

@@ -777,6 +777,7 @@ export class LGraphNode implements Positionable, IPinnable, IColorable {
     if (widgets && this.serialize_widgets) {
       o.widgets_values = []
       for (const [i, widget] of widgets.entries()) {
+        if (widget.serialize === false) continue
         // @ts-expect-error #595 No-null
         o.widgets_values[i] = widget ? widget.value : null
       }

src/types/widgets.ts

@@ -150,6 +150,12 @@ export interface IBaseWidget {
   type: TWidgetType
   value?: TWidgetValue
 
+  /**
+   * Whether the widget value should be serialized on node serialization.
+   * @default true
+   */
+  serialize?: boolean
+
   /**
    * The computed height of the widget. Used by customized node resize logic.
    * See scripts/domWidget.ts for more details.