multi: add lnutils to host fundamental utility functions

We also move the `fn/stream.go` into the package `lnutils`. Eventually
we will put all the [utility
functions](https://github.com/lightninglabs/taro/tree/main/chanutils)
into this package.

discovery/gossiper.go

@@ -18,10 +18,10 @@ import (
 	"github.com/lightningnetwork/lnd/batch"
 	"github.com/lightningnetwork/lnd/chainntnfs"
 	"github.com/lightningnetwork/lnd/channeldb"
-	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/keychain"
 	"github.com/lightningnetwork/lnd/kvdb"
 	"github.com/lightningnetwork/lnd/lnpeer"
+	"github.com/lightningnetwork/lnd/lnutils"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/multimutex"
@@ -1185,7 +1185,7 @@ func (d *AuthenticatedGossiper) sendBatch(annBatch []msgWithSenders,
 	// skip the filter and dedup logic below, and just send the
 	// announcements out to all our coonnected peers.
 	if isLocal {
-		msgsToSend := fn.Map(
+		msgsToSend := lnutils.Map(
 			annBatch, func(m msgWithSenders) lnwire.Message {
 				return m.msg
 			},

lnutils/README.md

@@ -0,0 +1,4 @@
+# `lnutils`
+
+This package provides fundamental types and utility functions that can be used
+by all other packages.

lnutils/stream.go

@@ -1,4 +1,4 @@
-package fn
+package lnutils
 
 // Map takes an input slice, and applies the function f to each element,
 // yielding a new slice.