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.
I expected the `InputFormatterProviderContext` would be a bit more consistent with `InputFormatterContext`.  Why does the provider need `ModelMetadata` information (but the formatter does not)?