lnwallet+contractcourt: gracefully handle auto force close post data loss

In this commit, update the start up logic to gracefully handle a
seemingly rare case. In this case, a peer detects local data loss with a
set of active HTLCs. These HTLCs then eventually expire (they may or may
not actually "exist"), causing a force close decision. Before this PR,
this attempt would fail with a fatal error that can impede start up.

To better handle such a scenario, we'll now catch the error when we fail
to force close due to entering the DLP and instead terminate the state
machine at the broadcast state. When a commitment transaction eventually
confirms, we'll play it as normal.

Fixes https://github.com/lightningnetwork/lnd/issues/7984

lnwallet/channel_test.go

@@ -7417,10 +7417,7 @@ func TestForceCloseFailLocalDataLoss(t *testing.T) {
 	// channel, we should fail as it isn't safe to force close a
 	// channel that isn't in the pure default state.
 	_, err = aliceChannel.ForceClose()
-	if err == nil {
-		t.Fatalf("expected force close to fail due to non-default " +
-			"chan state")
-	}
+	require.ErrorIs(t, err, ErrForceCloseLocalDataLoss)
 }
 
 // TestForceCloseBorkedState tests that once we force close a channel, it's