Strictness for Roact Components

[stravant]

Currently it's easy to accidentally forget .props. / .state. when reading data from Roact components. It would be nice if there were an easy way to enable strictness for components extended from Roact.Component so that you would get an error if you accidentally type self.foobar instead of self.props.foobar, rather than a nil which silently propagates forwards and likely causes issues later on.