Generate ServiceType

[yuusheng]

Currently, we don't export an interface to describe the service.

For example:

syntax = "proto3";

package hero;

service HeroesService { rpc FindOne(HeroById) returns (Hero); }

message HeroById { int32 id = 1; }

message Hero {
  int32 id = 1;
  string name = 2;
}

will generate:

// @generated by protoc-gen-es v2.2.3 with parameter "target=ts"
// @generated from file hero.proto (package hero, syntax proto3)
/* eslint-disable */

import type { GenFile, GenMessage, GenService } from "@bufbuild/protobuf/codegenv1";
import { fileDesc, messageDesc, serviceDesc } from "@bufbuild/protobuf/codegenv1";
import type { Message } from "@bufbuild/protobuf";

// ...message stuff

/**
 * @generated from service hero.HeroesService
 */
export const HeroesService: GenService<{
  /**
   * @generated from rpc hero.HeroesService.FindOne
   */
  findOne: {
    methodKind: "unary";
    input: typeof HeroByIdSchema;
    output: typeof HeroSchema;
  },
}> = /*@__PURE__*/
  serviceDesc(file_hero, 0);

I suppose we should also have a HeroesService interface

export interface HeroesService {
  FindOne(request: HeroById): Promise<Hero>;
}