Use GetPayloadBodies in our Engine Client (#12630)

* add it to our engine client

* lint

* add better debugging info

* temp debugging

* fix

* fix it

* pretty

* dumb bug

* Revert "pretty"

This reverts commit 6a6df3cc5f.

* Revert "fix it"

This reverts commit 73dc617bb0.

* Revert "fix"

This reverts commit 3aecdaac6d.

* Revert "temp debugging"

This reverts commit ffcd2c61a0.

* Revert "add better debugging info"

This reverts commit 96184e8567.

* raul's comment

* regression test

---------

Co-authored-by: Raul Jordan <raul@prysmaticlabs.com>

proto/engine/v1/json_marshal_unmarshal.go

@@ -678,5 +678,6 @@ func (b *ExecutionPayloadBodyV1) UnmarshalJSON(enc []byte) error {
 		transactions[i] = tx
 	}
 	b.Transactions = transactions
+	b.Withdrawals = decoded.Withdrawals
 	return nil
 }

proto/engine/v1/json_marshal_unmarshal_test.go

@@ -487,6 +487,32 @@ func TestPayloadIDBytes_MarshalUnmarshalJSON(t *testing.T) {
 	require.Equal(t, true, item == *res)
 }
 
+func TestExecutionPayloadBody_MarshalUnmarshalJSON(t *testing.T) {
+	pBody := &enginev1.ExecutionPayloadBodyV1{
+		Transactions: [][]byte{[]byte("random1"), []byte("random2"), []byte("random3")},
+		Withdrawals: []*enginev1.Withdrawal{
+			&enginev1.Withdrawal{
+				Index:          200,
+				ValidatorIndex: 20303,
+				Amount:         3200000000,
+				Address:        bytesutil.PadTo([]byte("junk"), 20),
+			},
+			&enginev1.Withdrawal{
+				Index:          200,
+				ValidatorIndex: 70303,
+				Amount:         3200000800,
+				Address:        bytesutil.PadTo([]byte("junk2"), 20),
+			},
+		},
+	}
+	enc, err := json.Marshal(pBody)
+	require.NoError(t, err)
+	res := &enginev1.ExecutionPayloadBodyV1{}
+	err = res.UnmarshalJSON(enc)
+	require.NoError(t, err)
+	require.DeepEqual(t, pBody, res)
+}
+
 func TestExecutionBlock_MarshalUnmarshalJSON_MainnetBlock(t *testing.T) {
 	newBlock := &enginev1.ExecutionBlock{}
 	require.NoError(t, newBlock.UnmarshalJSON([]byte(blockJson)))