Improve Components DisplayNames properties

[pacxiu]

Is your feature request related to a problem? Please describe.
Hi there,

sometimes I find it extremely difficult to properly debug base components in React Dev Tools due to lack of Display Name (I think this is it?). For smaller layouts it will not be an issue, however sometimes we can construct more complex ones using only components from theme-ui. Debugging those can be a little bit of pain as some sample React's component tree can look like:

Describe the solution you'd like
A little bit cleaner react's component tree to debug.

[dburles]

Related #817