Add fileExtension event_details for Generate Suggestions v2 events

We are interested in what is acceptance rate per language.
It was added to v1 in Change 430359.

Google-Bug-Id: b/322005035
Release-Notes: skip
Change-Id: I7fd6961b63da3fa83c924b8e7489cec6193282ed
diff --git a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
index b73145b..3d76c82 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
+++ b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
@@ -1370,6 +1370,7 @@
       uuid: this.generatedSuggestionId,
       type: 'suggest-fix',
       commentId: this.comment.id,
+      fileExtension: getFileExtension(this.comment.path ?? ''),
     });
     this.suggestionLoading = true;
     let suggestionResponse;
@@ -1396,6 +1397,7 @@
       commentId: this.comment.id,
       response: suggestionResponse.responseCode,
       numSuggestions: suggestionResponse.fix_suggestions.length,
+      fileExtension: getFileExtension(this.comment.path ?? ''),
       logProbability: suggestionResponse.fix_suggestions?.[0].log_probability,
     });
     const suggestion = suggestionResponse.fix_suggestions?.[0];