Generate clients into separate files

[timostamm]

At the moment, service clients are generated into a single file.

For example, the following .proto:

syntax = "proto3";
package spec;
import "protobuf-ts.proto";
import "google/protobuf/wrappers.proto";

service AllStyleService {
    option (ts.client) = CALL;
    option (ts.client) = RX;
    option (ts.client) = PROMISE;

    rpc Unary (google.protobuf.StringValue) returns (google.protobuf.Int32Value);
    rpc ServerStream (google.protobuf.StringValue) returns (stream google.protobuf.Int32Value);
    rpc ClientStream (stream google.protobuf.StringValue) returns (google.protobuf.Int32Value);
    rpc Bidi (stream google.protobuf.StringValue) returns (stream google.protobuf.Int32Value);
}

Generates a typescript file service-style-all.ts:

export const AllStyleService = new ServiceType("spec.AllStyleService", [
    { name: "Unary", options: {}, I: StringValue, O: Int32Value },
    { name: "ServerStream", serverStreaming: true, options: {}, I: StringValue, O: Int32Value },
    { name: "ClientStream", clientStreaming: true, options: {}, I: StringValue, O: Int32Value },
    { name: "Bidi", serverStreaming: true, clientStreaming: true, options: {}, I: StringValue, O: Int32Value }
]);

export interface IAllStyleServiceCallClient { /* ... */ }
export class AllStyleServiceCallClient implements IAllStyleServiceCallClient, ServiceInfo { /* ... */ }

export interface IAllStyleServiceRxClient { /* ... */ }
export class AllStyleServiceRxClient implements IAllStyleServiceRxClient, ServiceInfo { /* ... */ }

export interface IAllStyleServicePromiseClient { /* ... */ }
export class AllStyleServicePromiseClient implements IAllStyleServicePromiseClient, ServiceInfo { /* ... */ }

This has the following disadvantages:

• client names have to be suffixed to prevent name clashes
• removing / adding a second client style will change client names, breaking imports in other code
• if we start generating servers (gRPC server support for @grpc/grpc-js #52), the file will have even more symbols

Possible solution:

• generate individual files for each client style
• CALL => service-style-all.client.ts
• RX => service-style-all.rx-client.ts
• PROMISE => service-style-all.promise-client.ts
• keep same symbol name for the client: AllStyleServiceClient

TODO:

• generate individual files for each client style
• fix collision of ServerStyle.NONE and ClientStyle.NONE
• prevent file name clashes
• refactor for better readability