lnwallet: allow read-only access to HtlcView's HTLCs

Due to a recent refactor, the HTLCs are no longer an exported type.
Custom channels need access to those updates, so we provide them in a
read-only manner.

lnwallet/channel.go

@@ -2545,6 +2545,18 @@ type HtlcView struct {
 	FeePerKw chainfee.SatPerKWeight
 }
 
+// AuxOurUpdates returns the outgoing HTLCs as a read-only copy of
+// AuxHtlcDescriptors.
+func (v *HtlcView) AuxOurUpdates() []AuxHtlcDescriptor {
+	return fn.Map(newAuxHtlcDescriptor, v.OurUpdates)
+}
+
+// AuxTheirUpdates returns the incoming HTLCs as a read-only copy of
+// AuxHtlcDescriptors.
+func (v *HtlcView) AuxTheirUpdates() []AuxHtlcDescriptor {
+	return fn.Map(newAuxHtlcDescriptor, v.TheirUpdates)
+}
+
 // fetchHTLCView returns all the candidate HTLC updates which should be
 // considered for inclusion within a commitment based on the passed HTLC log
 // indexes.