refactor(core): split web entry from core (#6082)

This pr is trying to split `web` and `electron` entries from `core`. It allows more platform-related optimization to be addressed in each entry.
We should remove all browser/electron only codes from `core` eventually, this is the very first step for that.

packages/frontend/core/src/index.tsx

@@ -1,43 +1 @@
-import './polyfill/intl-segmenter';
-import './polyfill/request-idle-callback';
-import './polyfill/resize-observer';
-
-import { assertExists } from '@blocksuite/global/utils';
-import { StrictMode } from 'react';
-import { createRoot } from 'react-dom/client';
-
-import { App } from './app';
-import { setup } from './bootstrap/setup';
-import { performanceLogger } from './shared';
-
-const performanceMainLogger = performanceLogger.namespace('main');
-function main() {
-  performanceMainLogger.info('start');
-
-  // skip bootstrap setup for desktop onboarding
-  if (window.appInfo?.windowName !== 'onboarding') {
-    performanceMainLogger.info('setup start');
-    setup();
-    performanceMainLogger.info('setup done');
-  }
-
-  mountApp();
-}
-
-function mountApp() {
-  performanceMainLogger.info('import app');
-  const root = document.getElementById('app');
-  assertExists(root);
-  performanceMainLogger.info('render app');
-  createRoot(root).render(
-    <StrictMode>
-      <App />
-    </StrictMode>
-  );
-}
-
-try {
-  main();
-} catch (err) {
-  console.error('Failed to bootstrap app', err);
-}
+export * from './web';