refactor: extract posthandler package (celestiaorg#3055)

Another small refactor to make app.go more readable.

app/app.go

@@ -3,6 +3,7 @@ package app
 import (
 	"io"
 
+	"github.com/celestiaorg/celestia-app/app/posthandler"
 	"github.com/celestiaorg/celestia-app/x/mint"
 	mintkeeper "github.com/celestiaorg/celestia-app/x/mint/keeper"
 	minttypes "github.com/celestiaorg/celestia-app/x/mint/types"
@@ -23,7 +24,6 @@ import (
 	"github.com/cosmos/cosmos-sdk/version"
 	"github.com/cosmos/cosmos-sdk/x/auth"
 	authkeeper "github.com/cosmos/cosmos-sdk/x/auth/keeper"
-	"github.com/cosmos/cosmos-sdk/x/auth/posthandler"
 	authtx "github.com/cosmos/cosmos-sdk/x/auth/tx"
 	authtypes "github.com/cosmos/cosmos-sdk/x/auth/types"
 	"github.com/cosmos/cosmos-sdk/x/auth/vesting"
@@ -496,7 +496,7 @@ func New(
 		ante.DefaultSigVerificationGasConsumer,
 		app.IBCKeeper,
 	))
-	app.setPostHanders()
+	app.SetPostHandler(posthandler.New())
 
 	if loadLatest {
 		if err := app.LoadLatestVersion(); err != nil {
@@ -663,17 +663,6 @@ func (app *App) RegisterNodeService(clientCtx client.Context) {
 	nodeservice.RegisterNodeService(clientCtx, app.GRPCQueryRouter())
 }
 
-func (app *App) setPostHanders() {
-	postHandler, err := posthandler.NewPostHandler(
-		posthandler.HandlerOptions{},
-	)
-	if err != nil {
-		panic(err)
-	}
-
-	app.SetPostHandler(postHandler)
-}
-
 // BlockedParams are params that require a hardfork to change, and cannot be changed via
 // governance.
 func (*App) BlockedParams() [][2]string {

app/posthandler/posthandler.go

@@ -0,0 +1,12 @@
+package posthandler
+
+import (
+	sdk "github.com/cosmos/cosmos-sdk/types"
+)
+
+// New returns a new posthandler chain. Note: the Cosmos SDK does not export a
+// type for PostHandler so the AnteHandler type is used.
+func New() sdk.AnteHandler {
+	postDecorators := []sdk.AnteDecorator{}
+	return sdk.ChainAnteDecorators(postDecorators...)
+}