[Error Boundary] Correct type for stack property in widget-rendering-error:ti (#3045)

## Summary:
Remove "undefined" from stack property type definition.

Issue: LEMS-3714

Author: mark-fitzgerald

Reviewers: catandthemachines

Required Reviewers:

Approved By: catandthemachines

Checks: ⏭️  1 check has been skipped, ✅ 10 checks were successful

Pull Request URL: #3045

Author: mark-fitzgerald

.changeset/tricky-radios-grow.md

@@ -0,0 +1,5 @@
+---
+"@khanacademy/perseus-core": patch
+---
+
+[Error Boundary] Correct type for stack property in widget-rendering-error:ti

packages/perseus-core/src/analytics.ts

@@ -23,7 +23,7 @@ export type PerseusAnalyticsEvent =
               widgetType: string;
               widgetId: string;
               message: string;
-              stack: string | undefined;
+              stack: string;
               userAgent: string;
           };
       }

packages/perseus/src/widget-container.tsx

@@ -176,7 +176,9 @@ class WidgetContainer extends React.Component<Props, State> {
                                         widgetType: type,
                                         widgetId: this.props.id,
                                         message: error.message,
-                                        stack: error.stack,
+                                        stack:
+                                            error.stack ??
+                                            "No stack trace available",
                                         userAgent: userAgent,
                                     },
                                 });