Fix: Simplify the widget state logic (#6741)

## Summary

Fixes the case where a value is updated in the graph but the result
doesn't reflect on the widget representation on the relevant node.

## Changes

- **What**: Uses vanilla Vue utilities instead of a special utility
- **What**: Fewer places where state could be desynced.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6741-Fix-WIP-Simplify-the-widget-state-logic-2af6d73d36508160b729db50608a2ea9)
by [Unito](https://www.unito.io)

---------

Co-authored-by: github-actions <github-actions@github.com>

tests-ui/tests/renderer/extensions/vueNodes/widgets/components/WidgetSelectDropdown.test.ts

@@ -25,7 +25,7 @@ describe('WidgetSelectDropdown custom label mapping', () => {
       getOptionLabel?: (value: string | null) => string
     } = {},
     spec?: ComboInputSpec
-  ): SimplifiedWidget<string | number | undefined> => ({
+  ): SimplifiedWidget<string | undefined> => ({
     name: 'test_image_select',
     type: 'combo',
     value,
@@ -37,8 +37,8 @@ describe('WidgetSelectDropdown custom label mapping', () => {
   })
 
   const mountComponent = (
-    widget: SimplifiedWidget<string | number | undefined>,
-    modelValue: string | number | undefined,
+    widget: SimplifiedWidget<string | undefined>,
+    modelValue: string | undefined,
     assetKind: 'image' | 'video' | 'audio' = 'image'
   ): VueWrapper<WidgetSelectDropdownInstance> => {
     return mount(WidgetSelectDropdown, {