fix(runtime): 切换设计窗体大小时，同时修改app

runtime/react/playground/main.tsx

@@ -29,11 +29,16 @@ import plugins from '../.tmagic/plugin-entry';
 
 import App from './App';
 
+const designWidth = document.documentElement.getBoundingClientRect().width;
+
 const app = new Core({
+  designWidth,
   config: {},
   platform: 'editor',
 });
 
+window.appInstance = app;
+
 let curPageId = '';
 
 const updateConfig = (root: MApp) => {