Testnet address generation to wallet-wasm.

The motivation to change this part of the deprecated `wallet-wasm`
library was the simple introduction of testnet address support in
yoroi-mobile. The alternative is to migrate all of yoroi-mobile away to
use the new `cardano-wallet` module, but this would be significant work
in comparasin and can be delayed. Directly adapating
`react-native-cardano` to use `cardano-wallet` was not feasable either
as the API is quite different and would be exceptionally awkward to try
and force into the `react-native-cardano` API that was built on top of
`wallet-wasm` with its API in mind.

Only `xwallet_account()` was changed, as the other function lacking
support for testnet, `wallet_public_to_address()` does not seem to be used
anywhere in react-native-cardano, which was the motivation for this change.
Changing `wallet_public_to_address()` would also be more difficult as it
requires a hard API change or an additional function to allow
overloading.

On the other hand, `xwallet_account()` supports a JSON API,
which conveniently allows us to be backwards compatable, as the absence
of the `protocol_magic` field will revert to the previous behavior of
default (mainnet) protocol magic.

wallet-wasm/src/lib.rs

@@ -1058,6 +1058,8 @@ struct GenAddressesInput {
     account: Bip44Account,
     address_type: bip44::AddrType,
     indices: Vec<u32>,
+    // For backwards compatability, absence of this field means mainnet
+    protocol_magic: Option<cardano::config::ProtocolMagic>,
 }
 
 #[no_mangle]
@@ -1072,14 +1074,18 @@ pub extern "C" fn xwallet_addresses(
         output_ptr,
         account.change(input.account.derivation_scheme, input.address_type)
     );
+    let network_magic = match input.protocol_magic {
+        Some(pm) => cardano::config::NetworkMagic::from(pm),
+        None => default_network_magic(),
+    };
 
     let mut addresses: Vec<address::ExtendedAddr> = Vec::with_capacity(input.indices.len());
     for index in input.indices.into_iter() {
         let xpub = jrpc_try!(
             output_ptr,
             changelevel.index(input.account.derivation_scheme, index)
         );
-        let addr = address::ExtendedAddr::new_simple(*xpub, default_network_magic());
+        let addr = address::ExtendedAddr::new_simple(*xpub, network_magic);
         addresses.push(addr);
     }
     jrpc_ok!(output_ptr, addresses)