add intersection-observer polyfill

frontend/app/common/polyfills.ts

@@ -1,3 +1,4 @@
+import 'intersection-observer';
 import 'core-js/es/promise';
 import 'focus-visible';
 import '@webcomponents/custom-elements';

frontend/package-lock.json

@@ -6882,6 +6882,11 @@
       "integrity": "sha512-mT34yGKMNceBQUoVn7iCDKDntA7SC6gycMAWzGx1z/CMCTV7b2AAtXlo3nRyHZ1FelRkQbQjprHSYGwzLtkVbw==",
       "dev": true
     },
+    "intersection-observer": {
+      "version": "0.7.0",
+      "resolved": "https://registry.npmjs.org/intersection-observer/-/intersection-observer-0.7.0.tgz",
+      "integrity": "sha512-Id0Fij0HsB/vKWGeBe9PxeY45ttRiBmhFyyt/geBdDHBYNctMRTE3dC1U3ujzz3lap+hVXlEcVaB56kZP/eEUg=="
+    },
     "invariant": {
       "version": "2.2.4",
       "resolved": "https://registry.npmjs.org/invariant/-/invariant-2.2.4.tgz",

frontend/package.json

@@ -98,6 +98,7 @@
     "bem-react-helper": "^1.1.2",
     "core-js": "^3.1.4",
     "focus-visible": "^5.0.2",
+    "intersection-observer": "^0.7.0",
     "preact": "^8.4.2",
     "preact-redux": "^2.0.3",
     "redux": "^4.0.4",