Implement From<PendingV2Channel> for ChannelPhase

Exposing ChannelPhase in ChannelManager has led to verbose match
statements, which need to be modified each time a ChannelPhase is added.
Making ChannelPhase an implementation detail of Channel would help avoid
this.

As a step in this direction, define a conversion from PendingV2Channel
to ChannelPhase (to be renamed Channel).

Author: jkczyz

lightning/src/ln/channel.rs

@@ -1378,6 +1378,16 @@ where
 	}
 }
 
+impl<SP: Deref> From<PendingV2Channel<SP>> for ChannelPhase<SP>
+where
+	SP::Target: SignerProvider,
+	<SP::Target as SignerProvider>::EcdsaSigner: ChannelSigner,
+{
+	fn from(channel: PendingV2Channel<SP>) -> Self {
+		ChannelPhase::UnfundedV2(channel)
+	}
+}
+
 impl<SP: Deref> From<Channel<SP>> for ChannelPhase<SP>
 where
 	SP::Target: SignerProvider,

lightning/src/ln/channelmanager.rs

@@ -7713,7 +7713,7 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 								node_id: channel.context.get_counterparty_node_id(),
 								msg: channel.accept_inbound_dual_funded_channel()
 							};
-							(channel.context.channel_id(), ChannelPhase::UnfundedV2(channel), Some(message_send_event))
+							(channel.context.channel_id(), ChannelPhase::from(channel), Some(message_send_event))
 						})
 					},
 				}
@@ -7991,7 +7991,7 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 					node_id: *counterparty_node_id,
 					msg: channel.accept_inbound_dual_funded_channel(),
 				};
-				(ChannelPhase::UnfundedV2(channel), Some(message_send_event))
+				(ChannelPhase::from(channel), Some(message_send_event))
 			},
 		};