MediaWiki theme: RadioInputWidget tweaks
MediaWiki theme: RadioInputWidget tweaks

* Add a 'white-space: nowrap;' rule, like for checkbox.
* Use .oo-ui-transition() mixin.

Change-Id: Id600186ade0aff119d6c80fcef7d76e1180a9f66

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui