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.

[sffc]

Also note the new trait BoundDataProvider which is similar to DynamicDataProvider but it is actually useful in components.

[robertbastian]

DynamicDataProvider currently unifies code between BufferProvider aka DynamicDataProvider<BufferMarker>, and ExportableProvider, aka DynamicDataProvider<ExportMarker>. Ideally it would also do this for AnyMarker, but this doesn't currently work with yoke.