Make unsupported browser check asynchronous

This check is very expensive, and will pass almost 100% of the time.

Related #36728
Depends on #38329

Signed-off-by: Varun Patil <varunpatil@ucla.edu>

Author: pulsejet

core/src/unsupported-browser-redirect.js

@@ -19,8 +19,9 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-import { testSupportedBrowser } from './utils/RedirectUnsupportedBrowsers.js'
-
 if (!window.TESTING && !OC?.config?.no_unsupported_browser_warning) {
-	testSupportedBrowser()
+	window.addEventListener('DOMContentLoaded', async function() {
+		const { testSupportedBrowser } = await import('./utils/RedirectUnsupportedBrowsers.js')
+		testSupportedBrowser()
+	})
 }