Failed to compile when using google protobuf files

**Describe the bug**
https://github.com/cloudwego/kitex/issues/835
When importing google protobuf files, such as timestamp, those structs don't have fastpb interface, so users cannot compile codes.

**To Reproduce**

```
syntax = "proto3";

option go_package = "pbdemo";
import "google/protobuf/timestamp.proto";

package pbdemo;

service ServiceA {
rpc SayHello (Request) returns (Reply) {}
}

message Request {
string name = 1;
google.protobuf.Timestamp date = 4;
}

message Reply {
string message = 1;
}

```