Split GuildThread from GuildChannel

[GnomedDev]

This fixes #2991, via the solution voted for on the serenity discord.

[GnomedDev]

This is ready for review, the main changes are:

• GuildChannel is now:

• • BaseGuildChannel (shared fields)
• • GuildChannel (channel-exclusive)
• • GuildThread (thread-exclusive)
• • GenericGuildChannelRef (an enum over references to both)

• PartialChannel is now:

• • BaseInteractionChannel (shared fields)
• • InteractionChannel (channel-exclusive)
• • InteractionThread (thread-exclusive)
• • GenericInteractionChannel (an enum over the both)

• ChannelId is now:

• • GenericChannelId (shared purpose/methods)
• • ChannelId (channel-exclusive)
• • ThreadId (thread-exclusive)

The IDs have methods to convert between, such as:

• GenericChannelId::expect_channel and GenericChannelId::expect_thread which casts the ID types without touching the value
• GenericChannelId::split which calls both and returns both for when something needs to handle both cases
• ThreadId::widen and Channelid::widen which cast to GenericChannelId for when you have a specific ID and need to "widen" the number of methods you can call.

GenericGuildChannelRef is returned from the new Guild::channel method, which looks the GenericChannelId up in both Guild::channels and Guild::threads.

[jamesbt365]

This looks really good, not 100% sure if I like the name changes for PartialChannel, but I can't think of anything better right now so I think its passable.

[peanutbother]

I also think the naming could be improved since we are explicitly talking about channels and threads.
My proposal in discord was the following:

How about

enum MessageOrigin {
    Channel(ChannelId),
    Thread(ThreadId)
}

seems a better naming to me since I see Threads as their own thing so I would not name a message's origin a channel

In that naming scheme I would name Base* rather Origin* and in some contexts append or prepend Message* or Interaction* accordingly.

[GnomedDev]

@peanutbother I don't fully understand how this "origin" naming improves things? From how I processed that I think you are saying OriginGuildChannel which doesn't make too much sense, and we already have prepended Interaction where possible (as the other types are truly generically used everywhere).

[peanutbother]

I mean something like MessageOrigin and InteractionOrigin as base names instead of the chosen base names as for e.g. threads and channels the base name is still channel.