fix: Fix create metric fragment

The function `createEventFragment` of the `MetaMetricsController` was
broken recently in the migration to BaseControllerV2 (#28113). We ended
up trying to mutate a piece of Immer state, resulting in an error.

The affected line was updated to use `cloneDeep` prior to mutating,
so that we're no longer attempting to mutate a frozen object.

Fixes ##28599

app/scripts/controllers/metametrics-controller.ts

@@ -1,4 +1,5 @@
 import {
+  cloneDeep,
   isEqual,
   memoize,
   merge,
@@ -584,7 +585,8 @@ export default class MetaMetricsController extends BaseController<
       : {};
 
     this.update((state) => {
-      state.fragments[id] = merge(additionalFragmentProps, fragment);
+      // We're cloning "additionalFragmentProps" because it can contain a frozen piece of Immer state
+      state.fragments[id] = merge(cloneDeep(additionalFragmentProps), fragment);
     });
 
     if (fragment.initialEvent) {