Further subgraph improvements (#6466)

- Prune disconnected widgets on config panel open
- Fix breakage of DOMWidgets on double nest
- Fix self clipping of proxied DOMWidget nodes
- Blacklist cloning of promtoed widget prop

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6466-Further-subgraph-improvements-29c6d73d365081c8b63dda068486805c)
by [Unito](https://www.unito.io)

src/lib/litegraph/src/subgraph/SubgraphNode.ts

@@ -546,6 +546,7 @@ export class SubgraphNode extends LGraphNode implements BaseLGraph {
 
     // Clean up all promoted widgets
     for (const widget of this.widgets) {
+      if ('isProxyWidget' in widget && widget.isProxyWidget) continue
       this.subgraph.events.dispatch('widget-demoted', {
         widget,
         subgraphNode: this

src/lib/litegraph/src/widgets/BaseWidget.ts

@@ -140,6 +140,7 @@ export abstract class BaseWidget<TWidget extends IBaseWidget = IBaseWidget>
       displayValue,
       // @ts-expect-error Prevent naming conflicts with custom nodes.
       labelBaseline,
+      promoted,
       ...safeValues
     } = widget