Support cross domain/application copy/paste (#6087)

![AnimateDiff_00001](https://github.com/user-attachments/assets/8ae88dc5-bba8-40c0-9cc2-5e81f579761d)


Browsers place very heavy restrictions on what can be copied and pasted.
See:
- https://alexharri.com/blog/clipboard
- https://www.w3.org/TR/clipboard-apis/#mandatory-data-types-x

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6087-Experimental-cross-domain-application-copy-paste-28e6d73d36508154a0a8deeb392f43a4)
by [Unito](https://www.unito.io)

src/lib/litegraph/src/LGraphCanvas.ts

@@ -3867,11 +3867,10 @@ export class LGraphCanvas
    * When called without parameters, it copies {@link selectedItems}.
    * @param items The items to copy.  If nullish, all selected items are copied.
    */
-  copyToClipboard(items?: Iterable<Positionable>): void {
-    localStorage.setItem(
-      'litegrapheditor_clipboard',
-      JSON.stringify(this._serializeItems(items))
-    )
+  copyToClipboard(items?: Iterable<Positionable>): string {
+    const serializedData = JSON.stringify(this._serializeItems(items))
+    localStorage.setItem('litegrapheditor_clipboard', serializedData)
+    return serializedData
   }
 
   emitEvent(detail: LGraphCanvasEventMap['litegraph:canvas']): void {
@@ -3907,6 +3906,7 @@ export class LGraphCanvas
     if (!data) return
     return this._deserializeItems(JSON.parse(data), options)
   }
+
   _deserializeItems(
     parsed: ClipboardItems,
     options: IPasteFromClipboardOptions
@@ -3923,6 +3923,7 @@ export class LGraphCanvas
     const { graph } = this
     if (!graph) throw new NullGraphError()
     graph.beforeChange()
+    this.emitBeforeChange()
 
     // Parse & initialise
     parsed.nodes ??= []
@@ -4092,6 +4093,7 @@ export class LGraphCanvas
     this.selectItems(created)
 
     graph.afterChange()
+    this.emitAfterChange()
 
     return results
   }