Make feature = "v2" ⇒ pub send::V1Context (payjoin#604)

`v2::Sender::extract_v1(..) -> (.. v1::V1Context)`, so this type must
have public visibility in order for bindings to implement this
`extract_v1` function.

I decided not to make the v1 module public only with respect to this
V1Context type under exclusive v2 feature configuration because that
would introduce far more complexity. View code for exact semantics,
since `send::v1::V1Context` is still the path when the `v1` feature is
enabled.

Fix payjoin#599

Author: spacebear21

payjoin/src/send/mod.rs

@@ -35,6 +35,8 @@ pub(crate) mod v1;
 #[cfg(feature = "v2")]
 #[cfg_attr(docsrs, doc(cfg(feature = "v2")))]
 pub mod v2;
+#[cfg(all(feature = "v2", not(feature = "v1")))]
+pub use v1::V1Context;
 
 #[cfg(feature = "_multiparty")]
 pub mod multiparty;