Improve validation of request bodies for the following client-server API endpoints: [`/account/3pid/add`](https://spec.matrix.org/v1.3/client-server-api/#post_matrixclientv3account3pidadd), [`/account/3pid/bind`](https://spec.matrix.org/v1.3/client-server-api/#post_matrixclientv3account3pidbind), [`/account/3pid/delete`](https://spec.matrix.org/v1.3/client-server-api/#post_matrixclientv3account3piddelete) and [`/account/3pid/unbind`](https://spec.matrix.org/v1.3/client-server-api/#post_matrixclientv3account3pidunbind).