Use Matrix user profile image in avatar when running as a widget

[hughns]

Your use case

What would you like to do?

Show the Matrix user profile thumbnail for the user when using embedded mode.

Why would you like to do it?

Because it looks nicer and provides a more integrated experience.

How would you like to achieve it?

Add a new capability to the widget API that would allow the fetching of the media.

Have you considered any alternatives?

We used to have this capability, but it was removed as part of #2856 as the is currently no way to implement it whilst also using authenticated media.

An alternative would be to use unauthenticated media, but that is not desirable.

Additional context

No response