Update React Context to use `React.createContext`

# Issue summary

As part of `v4` we're changing our react context to use the new API. This issue is a list of what still needs to be done. All work should be done on the `version-4.0.0` branch.

* [x] AppProvider
* [x] withSticky
* [x] ComboBox
* [x] Navigation
* [x] Scrollable
* [x] ThemeProvider
* [x] ScrollLock
* [x] Sticky
