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/web/src/index.tsx

@@ -0,0 +1,45 @@
+import './polyfill/intl-segmenter';
+import './polyfill/request-idle-callback';
+import './polyfill/resize-observer';
+
+import { setup } from '@affine/core/bootstrap/setup';
+import { performanceLogger } from '@affine/core/shared';
+import { isDesktop } from '@affine/env/constant';
+import { StrictMode } from 'react';
+import { createRoot } from 'react-dom/client';
+
+import { App } from './app';
+
+const performanceMainLogger = performanceLogger.namespace('main');
+function main() {
+  performanceMainLogger.info('start');
+
+  // skip bootstrap setup for desktop onboarding
+  if (isDesktop && window.appInfo?.windowName === 'onboarding') {
+    performanceMainLogger.info('skip setup');
+  } else {
+    performanceMainLogger.info('setup start');
+    setup();
+    performanceMainLogger.info('setup done');
+  }
+
+  mountApp();
+}
+
+function mountApp() {
+  performanceMainLogger.info('import app');
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  const root = document.getElementById('app')!;
+  performanceMainLogger.info('render app');
+  createRoot(root).render(
+    <StrictMode>
+      <App />
+    </StrictMode>
+  );
+}
+
+try {
+  main();
+} catch (err) {
+  console.error('Failed to bootstrap app', err);
+}