Fix script error alert (#37458)

After using CSP nonce, the "onerror" doesn't work anymore. Change it to
use a global variable to detect

Also help users like #37379 to catch errors more easily.

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

web_src/js/globals.d.ts

@@ -53,6 +53,7 @@ interface Window {
     enableTimeTracking: boolean,
     mermaidMaxSourceCharacters: number,
     i18n: Record<string, string>,
+    frontendInited: boolean,
   },
   $: JQueryStatic,
   jQuery: JQueryStatic,