Use the resolved type name in generic strings, not the original

Use the resolved type name in generic strings, not the original

This makes some generics less readable, but some more, and reduces
generic type pollution. Some cases are a loss, eg
`Option_PaymentHashZ` gets converted to `Option_ThirtyTwoBytesZ`
(which less less readable but fewer total types as a result), but
we ultimately need this because we now have `schnorr::Signature`
and `ecdsa::Signature` so we can't rely on just using `Signature`
and having it be unique :(.