TextInput: ensure the field doesn’t lose focus when adornment is changed

[bpierre]

See aragon/client#904 (comment)

[2color]

After a closer look at this, this happens when going from no adornment to adornment. I presume it's to do with the wrapping div that we render for the adornment.

https://github.com/aragon/aragon-ui/blob/80e67f2cb10539a448bda4f9880d5f01cbd71cc2/src/components/Input/TextInput.js#L76-L85

I'm not sure how this should be resolved (is it possible to maintain focus if the underlying dom element has changed?).

For now, I've used the opacity css prop to avoid this problem.