[LDK Splicing]

In splicing, creation of the new funding tx is similar to the creation of the funding tx in the case of channel open.

But there is an important difference: in splicing, the new funding tx has the old funding tx as an input. Which means signing of the funding tx has to be done by both ends (as the prev funding tx is a 2-of-2 multisig).

It's not easy to accomplish this without the full tx negotiation messages.