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.

channeldb/migration29/migration_test.go

@@ -0,0 +1,67 @@
+package migration29
+
+import (
+	"testing"
+
+	"github.com/lightningnetwork/lnd/channeldb/migtest"
+	"github.com/lightningnetwork/lnd/kvdb"
+)
+
+var (
+	hexStr = migtest.Hex
+
+	outpoint1 = hexStr("81b637d8fcd2c6da6859e6963113a1170de793e4b725b84d1e0b4cf99ec58ce90fb463ad")
+	outpoint2 = hexStr("81b637d8fcd2c6da6859e6963113a1170de793e4b725b84d1e0b4cf99ec58ce952d6c6c7")
+
+	chanID1 = hexStr("81b637d8fcd2c6da6859e6963113a1170de793e4b725b84d1e0b4cf99ec5ef44")
+	chanID2 = hexStr("81b637d8fcd2c6da6859e6963113a1170de793e4b725b84d1e0b4cf99ec54a2e")
+
+	// These tlv streams are used to populate the outpoint bucket at the
+	// start of the test.
+	tlvOutpointOpen   = hexStr("000100")
+	tlvOutpointClosed = hexStr("000101")
+
+	// outpointData is used to populate the outpoint bucket.
+	outpointData = map[string]interface{}{
+		outpoint1: tlvOutpointOpen,
+		outpoint2: tlvOutpointClosed,
+	}
+
+	// chanIDBefore is the ChannelID bucket before the migration.
+	chanIDBefore = map[string]interface{}{}
+
+	// post is the expected data in the ChannelID bucket after the
+	// migration.
+	post = map[string]interface{}{
+		chanID1: "",
+		chanID2: "",
+	}
+)
+
+// TestMigrateChannelIDIndex asserts that the ChannelID index is properly
+// populated.
+func TestMigrateChannelIDIndex(t *testing.T) {
+	// Prime the database with the populated outpoint bucket. We create the
+	// ChannelID bucket since the prior migration creates it anyways.
+	before := func(tx kvdb.RwTx) error {
+		err := migtest.RestoreDB(tx, outpointBucket, outpointData)
+		if err != nil {
+			return err
+		}
+
+		return migtest.RestoreDB(tx, chanIDBucket, chanIDBefore)
+	}
+
+	// After the migration, ensure that the ChannelID bucket is properly
+	// populated.
+	after := func(tx kvdb.RwTx) error {
+		err := migtest.VerifyDB(tx, outpointBucket, outpointData)
+		if err != nil {
+			return err
+		}
+
+		return migtest.VerifyDB(tx, chanIDBucket, post)
+	}
+
+	migtest.ApplyMigration(t, before, after, MigrateChanID, false)
+}