feat(module): add support for vue using unplugin (#2416)

Co-authored-by: Benjamin Canac <canacb1@gmail.com>

src/runtime/vue/stubs.ts

@@ -0,0 +1,36 @@
+import { ref } from 'vue'
+import type { Ref, Plugin as VuePlugin } from 'vue'
+
+import appConfig from '#build/app.config'
+import type { NuxtApp } from '#app'
+
+export { useHead } from '@unhead/vue'
+export { useRoute, useRouter } from 'vue-router'
+
+export const useAppConfig = () => appConfig
+
+const state: Record<string, any> = {}
+
+export const useState = <T>(key: string, init: () => T): Ref<T> => {
+  if (state[key]) {
+    return state[key] as Ref<T>
+  }
+  const value = ref(init())
+  state[key] = value
+  return value as Ref<T>
+}
+
+export function useNuxtApp() {
+  return {
+    isHydrating: true,
+    payload: { serverRendered: false }
+  }
+}
+
+export function defineNuxtPlugin(plugin: (nuxtApp: NuxtApp) => void) {
+  return {
+    install(app) {
+      plugin({ vueApp: app } as NuxtApp)
+    }
+  } satisfies VuePlugin
+}