fix(core): guard reading of global `ngDevMode` for undefined. (#36055)

When reading globals such as `ngDevMode` the read should be guarded by `typeof ngDevMode` otherwise it will throw if not
defined in `"use strict"` mode.

PR Close #36055

packages/core/src/util/ng_dev_mode.ts

@@ -115,7 +115,7 @@ export function initNgDevMode(): boolean {
     if (typeof ngDevMode !== 'object') {
       ngDevModeResetPerfCounters();
     }
-    return !!ngDevMode;
+    return typeof ngDevMode !== 'undefined' && !!ngDevMode;
   }
   return false;
 }