fix(firestore): fix fetch connection error message

.changeset/lemon-flies-yawn.md

@@ -0,0 +1,5 @@
+---
+'@firebase/firestore': patch
+---
+
+Fixes fetch connection error messages that were undefined.

packages/firestore/src/platform/browser_lite/fetch_connection.ts

@@ -55,10 +55,21 @@ export class FetchConnection extends RestConnection {
       }
       response = await fetch(url, fetchArgs);
     } catch (e) {
-      const err = e as { status: number | undefined; statusText: string };
+      const err = e as {
+        message?: string;
+        status?: number;
+        statusText?: string;
+        cause?: unknown;
+      };
+      const message = err?.message;
+      const cause = err?.cause ? String(err.cause) : undefined;
+      const errorMessage =
+        (message && cause ? `${message} (${cause})` : (message ?? cause)) ??
+        err?.statusText ??
+        String(e);
       throw new FirestoreError(
-        mapCodeFromHttpStatus(err.status),
-        'Request failed with error: ' + err.statusText
+        mapCodeFromHttpStatus(err?.status),
+        `Request failed with error: ${errorMessage}`
       );
     }