splice: Add plugin for magic “splice all” command

The command called “splice” can take a json payload or a ‘splice script’, process it into a list of ‘actions’ and then execute those actions.

These actions include or will include everything you would want to do with a splice:
* Splice into a channel
* Splice out of a channel
* Fund from wallet
* Deposit to wallet
* Send funds to bitcoin address

Changelog-Added: A new magic “splice” command is added that can take a ‘splice script’ or json payload and perform any complex splice across multiple channels merging the result into a single transaction. Some features are disabled and will be added in time.

plugins/Makefile

@@ -48,13 +48,15 @@ PLUGIN_SPENDER_SRC :=				\
 	plugins/spender/main.c			\
 	plugins/spender/multifundchannel.c	\
 	plugins/spender/multiwithdraw.c		\
-	plugins/spender/openchannel.c
+	plugins/spender/openchannel.c		\
+	plugins/spender/splice.c
 PLUGIN_SPENDER_HEADER :=			\
 	plugins/spender/multifundchannel.h	\
 	plugins/spender/multiwithdraw.h		\
 	plugins/spender/fundchannel.h		\
 	plugins/spender/multifundchannel.h	\
-	plugins/spender/openchannel.h
+	plugins/spender/openchannel.h		\
+	plugins/spender/splice.h
 PLUGIN_SPENDER_OBJS := $(PLUGIN_SPENDER_SRC:.c=.o)
 
 PLUGIN_FUNDER_SRC :=				\
@@ -164,6 +166,7 @@ PLUGIN_COMMON_OBJS :=				\
 	common/pseudorand.o			\
 	common/random_select.o			\
 	common/scb_wiregen.o			\
+	common/splice_script.o			\
 	common/setup.o				\
 	common/status_levels.o			\
 	common/type_to_string.o			\

plugins/spender/main.c

@@ -3,6 +3,7 @@
 #include <plugins/spender/multifundchannel.h>
 #include <plugins/spender/multiwithdraw.h>
 #include <plugins/spender/openchannel.h>
+#include <plugins/spender/splice.h>
 
 /*~ The spender plugin contains various commands that handle
  * spending from the onchain wallet.  */
@@ -27,6 +28,7 @@ int main(int argc, char **argv)
 	tal_expand(&commands, multiwithdraw_commands, num_multiwithdraw_commands);
 	tal_expand(&commands, fundchannel_commands, num_fundchannel_commands);
 	tal_expand(&commands, multifundchannel_commands, num_multifundchannel_commands);
+	tal_expand(&commands, splice_commands, num_splice_commands);
 	/* tal_expand(&commands, whatever_commands, num_whatever_commands); */
 
 	notifs = tal_arr(NULL, struct plugin_notification, 0);