Subgraph widget promotion fixes (#5911)

- Fixes automatic promotion of image previews by ~~more correctly
handling a usage of `requestAnimationFrame` and~~ introducing a means to
perform actions upon successful load of preview.
- When workflows contain an old proxyWidget property in string form,
parse it instead of throwing an error.
- Do not overlay the `label` of promoted widgets. Further consideration
is needed, but this resolves the primary annoyance and prevents
untranslated widget names
See #5914

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5911-Subgraph-widget-promotion-fixes-2826d73d365081838ffeeea4b8d7068c)
by [Unito](https://www.unito.io)

src/core/graph/subgraph/proxyWidgetUtils.ts

@@ -119,9 +119,15 @@ export function promoteRecommendedWidgets(subgraphNode: SubgraphNode) {
   const interiorNodes = subgraphNode.subgraph.nodes
   for (const node of interiorNodes) {
     node.updateComputedDisabled()
-    //NOTE: Since this operation is async, previews still don't exist after the single frame
-    //Add an onLoad callback to updatePreviews?
-    updatePreviews(node)
+    function checkWidgets() {
+      updatePreviews(node)
+      const widget = node.widgets?.find((w) => w.name.startsWith('$$'))
+      if (!widget) return
+      const pw = getProxyWidgets(subgraphNode)
+      if (pw.some(matchesPropertyItem([node, widget]))) return
+      promoteWidget(node, widget, [subgraphNode])
+    }
+    requestAnimationFrame(() => updatePreviews(node, checkWidgets))
   }
   const filteredWidgets: WidgetItem[] = interiorNodes
     .flatMap(nodeWidgets)