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/polyfill/request-idle-callback.ts

@@ -0,0 +1,19 @@
+window.requestIdleCallback =
+  window.requestIdleCallback ||
+  function (cb) {
+    const start = Date.now();
+    return setTimeout(function () {
+      cb({
+        didTimeout: false,
+        timeRemaining: function () {
+          return Math.max(0, 50 - (Date.now() - start));
+        },
+      });
+    }, 1);
+  };
+
+window.cancelIdleCallback =
+  window.cancelIdleCallback ||
+  function (id) {
+    clearTimeout(id);
+  };