channeldb: BigSize migration, store zero-conf, scid-alias bits

This introduces a BigSize migration that is used to expand the width
of the ChannelStatus and ChannelType fields. Three channel "types"
are added - ZeroConfBit, ScidAliasChanBit, and ScidAliasFeatureBit.
ScidAliasChanBit denotes that the scid-alias channel type was
negotiated for the channel. ScidAliasFeatureBit denotes that the
scid-alias feature bit was negotiated during the *lifetime* of the
channel. Several helper functions on the OpenChannel struct are
exposed to aid callers from different packages.

The RefreshShortChanID has been renamed to Refresh.

A new function BroadcastHeight is used to guard access to the
mutable FundingBroadcastHeight member. This prevents data races.

funding/manager.go

@@ -2306,7 +2306,7 @@ func (f *Manager) waitForFundingConfirmation(
 	numConfs := uint32(completeChan.NumConfsRequired)
 	confNtfn, err := f.cfg.Notifier.RegisterConfirmationsNtfn(
 		&txid, fundingScript, numConfs,
-		completeChan.FundingBroadcastHeight,
+		completeChan.BroadcastHeight(),
 	)
 	if err != nil {
 		log.Errorf("Unable to register for confirmation of "+
@@ -2392,7 +2392,8 @@ func (f *Manager) waitForTimeout(completeChan *channeldb.OpenChannel,
 	defer epochClient.Cancel()
 
 	// On block maxHeight we will cancel the funding confirmation wait.
-	maxHeight := completeChan.FundingBroadcastHeight + maxWaitNumBlocksFundingConf
+	broadcastHeight := completeChan.BroadcastHeight()
+	maxHeight := broadcastHeight + maxWaitNumBlocksFundingConf
 	for {
 		select {
 		case epoch, ok := <-epochClient.Epochs:
@@ -2738,7 +2739,7 @@ func (f *Manager) annAfterSixConfs(completeChan *channeldb.OpenChannel,
 		// funding transaction reaches at least 6 confirmations.
 		confNtfn, err := f.cfg.Notifier.RegisterConfirmationsNtfn(
 			&txid, fundingScript, numConfs,
-			completeChan.FundingBroadcastHeight,
+			completeChan.BroadcastHeight(),
 		)
 		if err != nil {
 			return fmt.Errorf("unable to register for "+