A data layer that stores key-value pairs to persistent storage.

The data layer is a simple key-value store that can be used to store data that needs to be included in every Sst.trackEvent call. The data layer is stored in the application's data store, and can be accessed using the add, all, clear, contains, get, and remove methods.

The data layer is implemented as a singleton, and is accessed using the Sst.dataLayer property.