ConnectEthereum is the first place we're actually using the loading variant; before this point, I hadn't really implemented it.
This diff implements the loading variant with a loading spinner that is absolutely-positioned over the normal content.
The reason I took that approach is to avoid issues with the height changing. This way I don't have to worry about calculating the height of the text, or forcing the height of the text to be something specific.
Depends on D7845