fix(browser): Remove usage of Array.at() method (#16647)

Sentry SDK supported browsers:
https://docs.sentry.io/platforms/javascript/troubleshooting/supported-browsers/

`.at` is ES2022:
https://blog.saeloun.com/2022/02/24/ecmascript2022-adds-add-method/

The browser SDK supports ES2021 at the current moment, so we need to
change this.

Resolves #16646

Author: AbhiPrasad

packages/browser-utils/src/metrics/web-vitals/lib/LayoutShiftManager.ts

@@ -30,7 +30,8 @@ export class LayoutShiftManager {
     if (entry.hadRecentInput) return;
 
     const firstSessionEntry = this._sessionEntries[0];
-    const lastSessionEntry = this._sessionEntries.at(-1);
+    // This previously used `this._sessionEntries.at(-1)` but that is ES2022. We support ES2021 and earlier.
+    const lastSessionEntry = this._sessionEntries[this._sessionEntries.length - 1];
 
     // If the entry occurred less than 1 second after the previous entry
     // and less than 5 seconds after the first entry in the session,