Add InteractionMessage and InteractionMessageAccessor abstractions

[alikindsys]

InteractionMessage:
implspec:

concept: interface delegation
class InteractionMessage "imsg" : delegate(DiscordMessage)
val Interaction owner
override DiscordMessage.Edit():
    intr.Modify
override DiscordMessage.Delete():
    intr.Remove
async waitDelete()
async waitEdit()
async waitReaction{Toggle|Add|Remove}(pred?)
event OnEdit
event OnDelete
event OnReaction{Toggle|Add|Remove}

class Interaction:
async InteractionMessage SendMessage()
async InteractionMessage GetUserResponse()

void Dispatch() {
    foreach(message) if(message.wants(event)) message.Dispatch(event)
}

example usages:

intr.Origin.OnReactToggle += async (e) => ...
// instead of
intr.OnOriginReactToggle += ...

var imsg = await intr.SendMessageAsync();
imsg.AddReaction(":trash:");
imsg.OnReactionToggle += async (e) => {
    if (e.Emoji != ":trash:") return;
    ismg.Delete();
}

---

InteractionMessageAccessor:
implspec:

class InteractionMessageAccessor:
val Interaction owner
event On...
    ...
async Wait...
    ...
void Dispatch(EventArgs)

class ListInteractionAccessor : InteractionMessageAccessor:
mode = User | Bot | All
List<InteractionMessage> Get();
SingleAccessor First, Last

class SingleInteractionAccessor : InteractionMessageAccessor:
val ListAccessor parent
mode = First | Last
InteractionMessage Get();

class Interaction:
ListAccessor BotMessages
ListAccessor UserMessages
ListAccessor AllMessages
SingleAccessor Origin = UserMessages.First
SingleAccessor LatestMessage = AllMessages.Last

void Interaction.Dispatch {
    ...
    foreach (accessor) if (accessor.wants(event)) accessor.Dispatch(event)
}

example usages:

intr.UserMessages.Last.OnReactionAdd += ...
// NOT the same as
var imsg = ... // get latest user message
imsg.OnReactionAdd += ...