gen: sugared RPC request builder

[tdakkota]

For now use to make request we have to write something like:

	_, err = invoker.MessagesSendMedia(ctx, &tg.MessagesSendMediaRequest{
		Peer: &tg.InputPeerChannel{
			ChannelID:  ch.ID,
			AccessHash: ch.AccessHash,
		},
		Media: &tg.InputMediaUploadedDocument{
			File: f,
			Attributes: []tg.DocumentAttributeClass{
				&tg.DocumentAttributeFilename{FileName: "video.mp4"},
			},
		},
		RandomID: id,
	})

and there are some problems

• You need to write MessagesSendMedia(ctx, ...) instead of

  messages := client.Messages(tgs.Ctx(ctx))
  messages.SendMedia(...).Do()

  or

  messages := client.Messages()
  messages.SendMedia(...).DoCtx(ctx)

• You need to write types tg.InputMediaUploadedDocument or tg.MessagesSendMediaRequest instead of pretty methods like SendMedia or UploadedDocument.

• You need to fill fields like RandomID manually, but it can be filled automatically using given RandomIDSource

• Field Peer can be using different structures, so we can use mappers from gen: mappers for similar types #144 to provide multiple filling methods

• Some classes in schema have a empty constructor which can be used by default, for example InputMessagesFilterEmpty

• We can use zero values as valid fields in some cases even if these fields required by schema, for example message.sendMedia does not really require non-empty message field.

Finally, the sugared RPC call would be like

rpc.Messages(tgs.Ctx(ctx), tgs.ID(rand.Reader)).
  SendMedia().
  PeerChannel(id, hash).
  MediaDocument(f).Do()

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[tdakkota]

We decided that making it is better to make user-friendly helpers for concreate workflows rather than just sugaring Telegram API.