[Refactor] Move isImageNode to litegraphUtil (#2450)

src/utils/litegraphUtil.ts

@@ -0,0 +1,10 @@
+import type { IWidget, LGraphNode } from '@comfyorg/litegraph'
+
+export function isImageNode(node: LGraphNode) {
+  return (
+    node.imgs ||
+    (node &&
+      node.widgets &&
+      node.widgets.findIndex((obj: IWidget) => obj.name === 'image') >= 0)
+  )
+}