Summary:
Automatically provides and subscribes to dimension updates - super easy usage:
```
function MyComponent(props: Props) {
const {width, height, scale, fontScale} = useWindowDimensions();
return <Text ...
};
```
Only window for now - it's what people want 99% of the time, so we'll just shovel out a pit of success for them...
There are still cases where `Dimensions` is needed outside of React component render functions, like in GraphQL variables, so we need to keep the existing module.
Reviewed By: zackargyle
Differential Revision: D16525189
fbshipit-source-id: 0a049fb3be8d92888a8a69e3898d337b93422a09
5ec382d1be