Remove DynamicDataProvider and expand methods into ExportableProvider

[sffc]

I'm pretty sure that we're not using DynamicDataProvider anywhere except in the bounds of ExportableProvider.

We should merge DynamicDataProvider and IterableDynamicDataProvider into ExportableProvider in 2.0.

[robertbastian]

I see DynamicDataProvider as a core provider type, it's the equivalent to DataProvider where the key is only known at runtime. In fact, AnyProvider and BufferProvider should be instantiations of DynamicDataProvider for AnyMarker and BufferMarker.