Assign values to RecoveryId

[Kixunil]

Currently we have just the names making the values implicit. This is not strictly wrong but it really feels like implicit property even though we actually explicitly want the values to behave as they are written. Assigning explicit values (Zero = 0 etc) makes that intention clear.

We can also use as instead of match in the From impl to convey that this is intentional. (Might also help with debug performance.)