Support ics20 transfer msg memo field without changing cosmwasm-std.

Cosmwasm does not support a memo field in IBCMsg.TransferMsg and won't
until cosmwasm v2. This patch allows using the channel id as an optional
comma delimited string to piggyback a memo string. See:
CosmWasm/cosmwasm#1477

x/wasm/keeper/handler_plugin_encoders.go

@@ -3,6 +3,7 @@ package keeper
 import (
 	"encoding/json"
 	"fmt"
+	"strings"
 
 	wasmvmtypes "github.com/CosmWasm/wasmvm/types"
 	codectypes "github.com/cosmos/cosmos-sdk/codec/types"
@@ -277,14 +278,16 @@ func EncodeIBCMsg(portSource types.ICS20TransferPortSource) func(ctx sdk.Context
 			if err != nil {
 				return nil, sdkerrors.Wrap(err, "amount")
 			}
+			channelID, memo, _ := strings.Cut(msg.Transfer.ChannelID, ",")
 			msg := &ibctransfertypes.MsgTransfer{
 				SourcePort:       portSource.GetPort(ctx),
-				SourceChannel:    msg.Transfer.ChannelID,
+				SourceChannel:    channelID,
 				Token:            amount,
 				Sender:           sender.String(),
 				Receiver:         msg.Transfer.ToAddress,
 				TimeoutHeight:    ConvertWasmIBCTimeoutHeightToCosmosHeight(msg.Transfer.Timeout.Block),
 				TimeoutTimestamp: msg.Transfer.Timeout.Timestamp,
+				Memo:             memo,
 			}
 			return []sdk.Msg{msg}, nil
 		default: