report: Provide user information for browser-side errors.

b4dd118aa1 changed how the `user_info_str` parsed information out of
the events it received -- but only changed the server errors, not the
browser errors, though both use the same codepath.  As a result, all
browser errors since then have been incorrectly marked as being for
anonymous users.

Build and pass in the expected `user` dict into the event.

zerver/lib/error_notify.py

@@ -81,9 +81,8 @@ Deployed version: {version}
 
 
 def zulip_browser_error(report: Dict[str, Any], error_bot_email: str) -> None:
-    email_subject = "JS error: {user_email}".format(**report)
-
     user_info = user_info_str(report)
+    email_subject = f"JS error: {user_info}"
 
     body = f"User: {user_info}\n"
     body += "Message: {message}\n".format(**report)