feat(plugin): add vue example (#3592)

plugins/vue-hello-world/src/app.vue

@@ -0,0 +1,13 @@
+<script setup lang="ts">
+import { ref } from 'vue';
+
+const count = ref(0);
+</script>
+
+<template>
+  <el-button @click="count++">
+    {{ count }}
+  </el-button>
+</template>
+
+<style scoped></style>

plugins/vue-hello-world/src/global.d.ts

@@ -0,0 +1,5 @@
+declare module '*.vue' {
+  import type { ComponentOptions } from 'vue';
+  const component: ComponentOptions;
+  export default component;
+}

plugins/vue-hello-world/src/index.ts

@@ -0,0 +1,18 @@
+import type { PluginContext } from '@affine/sdk/entry';
+import ElementPlus from 'element-plus';
+import { createApp } from 'vue';
+
+import App from './app.vue';
+
+export const entry = (context: PluginContext) => {
+  context.register('headerItem', div => {
+    const app = createApp(App);
+    app.use(ElementPlus);
+    app.mount(div, false, false);
+    return () => {
+      app.unmount();
+    };
+  });
+
+  return () => {};
+};