contractcourt: add Launch method to anchor/breach resolver

We will use this and its following commits to break the original
`Resolve` methods into two parts - the first part is moved to a new
method `Launch`, which handles sending a sweep request to the sweeper.
The second part remains in `Resolve`, which is mainly waiting for a
spending tx.

Breach resolver currently doesn't do anything in its `Launch` since the
sweeping of justice outputs are not handled by the sweeper yet.

contractcourt/contract_resolver.go

@@ -10,6 +10,7 @@ import (
 	"github.com/btcsuite/btclog/v2"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/fn/v2"
+	"github.com/lightningnetwork/lnd/sweep"
 )
 
 var (
@@ -109,6 +110,15 @@ type contractResolverKit struct {
 	log btclog.Logger
 
 	quit chan struct{}
+
+	// sweepResultChan is the result chan returned from calling
+	// `SweepInput`. It should be mounted to the specific resolver once the
+	// input has been offered to the sweeper.
+	sweepResultChan chan sweep.Result
+
+	// launched specifies whether the resolver has been launched. Calling
+	// `Launch` will be a no-op if this is true.
+	launched bool
 }
 
 // newContractResolverKit instantiates the mix-in struct.