add small dom utility to resolve the dom node from a ref

packages/@headlessui-vue/src/utils/dom.ts

@@ -0,0 +1,7 @@
+import { Ref } from 'vue'
+
+export function dom<T extends HTMLElement>(ref?: Ref<T | null>): T | null {
+  if (ref == null) return null
+  if (ref.value == null) return null
+  return ((ref as Ref<T & { $el: unknown }>).value.$el ?? ref.value) as T | null
+}