In this commit, we modify the RecordT type to allow callers to re-use
the Record definition of a different type, but use the new type param to
override the integer type used on the wire.
This will let use do things like encode a signature using the same
RecordProducer instance, but with a diff type in another context.
The upcoming use for this is allowing our `lnwire.Sig` type to be
encoded in the same message using distinct TLV integer types (new co-op
close protocol).
Olaoluwa Osuntokun
66cf4396a2