Serialize NodeInputSlot.widget (#622)

Serialize linked widget on node input slot properly according to current
save format in
76818b54e6/src/extensions/core/widgetInputs.ts

src/utils/object.ts

@@ -0,0 +1,5 @@
+export function omitBy<T extends object>(obj: T, predicate: (value: any) => boolean): Partial<T> {
+  return Object.fromEntries(
+    Object.entries(obj).filter(([_key, value]) => !predicate(value)),
+  ) as Partial<T>
+}