Add default fontSize for Text components.

[RafalFilipek]

<ConfigBox unit="rem" baseSize={32}>
  // ...
  <Text>hello</Text> // this one is not working :/
  // ...
  <Text fontSize={1}>hello</Text> // 32px
</ConfigBox>

Right now you can set defaultTextStyles to make it work

const textStyles = {
  fontSize: 1,
};
// ...
<CofigBox defaultTextStyles={textStyles} />