channeld: Code to implement splicing

Update the lightningd <-> channeld interface with lots of new commands to needed to facilitate spicing.

Implement the channeld splicing protocol leveraging the interactivetx protocol.

Implement lightningd’s channel_control to support channeld in its splicing efforts.

Changelog-Added: Added the features to enable splicing & resizing of active channels.

channeld/Makefile

@@ -53,6 +53,7 @@ CHANNELD_COMMON_OBJS :=				\
 	common/status_wiregen.o			\
 	common/gossip_store.o			\
 	common/hmac.o				\
+	common/interactivetx.o			\
 	common/htlc_state.o			\
 	common/htlc_trim.o			\
 	common/htlc_tx.o			\
@@ -73,6 +74,7 @@ CHANNELD_COMMON_OBJS :=				\
 	common/ping.o				\
 	common/psbt_keypath.o		\
 	common/psbt_open.o			\
+	common/psbt_internal.o			\
 	common/private_channel_announcement.o	\
 	common/pseudorand.o			\
 	common/read_peer_msg.o			\