Implement Script for Witness and Add Tweak in PSBT.

Adding Witness Script and key tweaks makes
a Partially Signed Bitcoin Transaction the single data
source needed for a Signer to produce valid signatures.
A Signer is not required to be able to generate L2 keys,
e.g delayed payment basepoint.

Author: yellowred

lightning/src/chain/channelmonitor.rs

@@ -4289,6 +4289,7 @@ impl<Signer: WriteableEcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 						revocation_pubkey: broadcasted_holder_revokable_script.2,
 						channel_keys_id: self.channel_keys_id,
 						channel_value_satoshis: self.channel_value_satoshis,
+						channel_transaction_parameters: Some(self.onchain_tx_handler.channel_transaction_parameters.clone()),
 					}));
 				}
 			}

lightning/src/ln/channel_keys.rs

@@ -37,14 +37,30 @@ macro_rules! basepoint_impl {
 			pub fn to_public_key(&self) -> PublicKey {
 				self.0
 			}
+
+			/// Derives a per-commitment-transaction (eg an htlc key or delayed_payment key) private key addition tweak
+			/// from a basepoint and a per_commitment_point:
+			/// `privkey = basepoint_secret + SHA256(per_commitment_point || basepoint)`
+			/// This calculates the hash part in the tweak derivation process, which is used to ensure
+			/// that each key is unique and cannot be guessed by an external party. It is equivalent
+			/// to the `from_basepoint` method, but without the addition operation, providing just the
+			/// tweak from the hash of the per_commitment_point and the basepoint.
+			pub fn derive_add_tweak(
+				&self,
+				per_commitment_point: &PublicKey,
+			) -> [u8; 32] {
+				let mut sha = Sha256::engine();
+				sha.input(&per_commitment_point.serialize());
+				sha.input(&self.to_public_key().serialize());
+				Sha256::from_engine(sha).to_byte_array()
+			}
 		}
 
 		impl From<PublicKey> for $BasepointT {
 			fn from(value: PublicKey) -> Self {
 				Self(value)
 			}
 		}
-
 	}
 }
 macro_rules! key_impl {