TS Top Level Enums are not imported correctly

[rogchap]

As a result of: #433

@shaxbee Firstly, thank you for this PR, makes for much better typings.

I've noticed that this has caused a side-effect with importing top level enums that are imported; messages seem to be correctly referenced but enums are not. In the below example I would expect Status to be status_pb.Status in the *.d.ts

Input:

// echo.proto
syntax = "proto3";

package grpc.gateway.testing;
import "status.proto";

message EchoStatusRequest {
  Status status = 1;
  StatusMessage msg = 2;
}

// status.proto
syntax = "proto3";

package grpc.gateway.testing;

enum Status {
  UNKNOWN = 0;
  SUCCESS = 1;
}

message StatusMessage {
  string status = 1;
}

Output:

// echo_pb.d.ts
import * as status_pb from './status_pb';

export class EchoStatusRequest {
  constructor ();
  getStatus(): Status;
  setStatus(a: Status): void;
  getMsg(): status_pb.StatusMessage;
  setMsg(a: status_pb.StatusMessage): void;
  toObject(): EchoStatusRequest.AsObject;
  serializeBinary(): Uint8Array;
  static deserializeBinary: (bytes: {}) => EchoStatusRequest;
}

export namespace EchoStatusRequest {
  export type AsObject = {
    status: Status;
    msg: status_pb.StatusMessage;
  }
}

[shaxbee]

Thanks for finding this ;-)