refactor(infra): directory structure (#4615)

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

@@ -0,0 +1,32 @@
+import type { PluginContext } from '@affine/sdk/entry';
+import { createElement } from 'react';
+import { lazy } from 'react';
+import { createRoot } from 'react-dom/client';
+
+const HeaderItem = lazy(() =>
+  import('./app').then(({ HeaderItem }) => ({ default: HeaderItem }))
+);
+
+export const entry = (context: PluginContext) => {
+  console.log('register');
+  console.log('hello, world!');
+  context.register('headerItem', div => {
+    const root = createRoot(div);
+    root.render(createElement(HeaderItem));
+    return () => {
+      root.unmount();
+    };
+  });
+
+  context.register('formatBar', div => {
+    const root = createRoot(div);
+    root.render(createElement(HeaderItem));
+    return () => {
+      root.unmount();
+    };
+  });
+
+  return () => {
+    console.log('unregister');
+  };
+};