This fixes a common React warning we see. Most of these components should be using constructors instead, however componentDidMount is just as good (and doesn't require converting most of these).
Conversion to classes will be done in a later stage of React warning fixes.
For https://github.com/vector-im/riot-web/issues/12877
We use `export default` begrudgingly here. Ideally we'd use just `export`, though this entire SDK expects things to be exported as a default. Instead of breaking everything, we'll sacrifice our export pattern for a smaller diff - a later commit can always do the default export -> regular export conversion.
