IInputFormatter interface changes. 

1. Moving input formatting related classes to MVC Core.(for tests as well).
2. Cleaning up the IInputFormatter to the final version.
3. Updating the input formatters and the context to be compliant with the IInputFormatter interface.

- Not cleaning up TempInputFormatterProvider.
Only when there are no encodings registered for this formatter ( which practically speaking is never, don't really see users updating the supported encodings.).