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.

tools/generate-wire.py

@@ -231,6 +231,7 @@ class Type(FieldSet):
         'failed_htlc',
         'existing_htlc',
         'simple_htlc',
+        'inflight',
         'utxo',
         'bitcoin_tx',
         'wirestring',