feat/refactor(Channels): Restructure channel classes, text in stage support

[bsian03]

TODO:

• JSDoc
• Typings
• toJSON methods
• Merge ForumChannel
• createGroupChannel proper support
• ThreadMember guildMember remove REST note
• Remove the console log from Channel
• Check discord-api-docs PRs for undocumented props needing to be added

BREAKING CHANGES:

• TextVoiceChannel removed
• Channel#client is now hidden (renamed Channel#_client)
• DMChannel#recipient (formerly PrivateChannel) is now recipients as a collection with a single entry (or supposed to)

Channel structure is now:

• Channel
  • DMChannel
  • GroupChannel
  • GuildChannel
    • CategoryChannel
    • ForumChannel
    • GuildTextableChannel
      • TextChannel
        • NewsChannel
      • VoiceChannel
        • StageChannel
      • ThreadChannel
        • PrivateThreadChannel
        • PublicThreadChannel
        • NewsThreadChannel

With this change, only methods/properties relevant to the class/structure will be present. All others have been removed without deprecation

Features

• GuildTextableChannel class - acts as a "middleman" class for common props/methods across all kinds of guild channels where you can send messages in
• Group Channel changes:
  • Unmarked user account flag for relevant methods
  • Actual support for adding users to group channel (requires OAuth gdm.join scope)
• Document content.nonce for messages
• getThreadMember endpoint

Fixes

• Docs:
  • deleteChannel return type
• ThreadMember#guildMember is now populated (consider renaming to just member?)

Deprecations

• PrivateChannel -> DMChannel
• Client#privateChannelMap -> Client#dmChannelMap
• Client#privateChannels -> Client#dmChannels

(note this is probably out of date)

[bsian03]

Heck. I'll resolve these voice things for now and do a find all and replace at some point

[bsian03]

Status update: Typings are done updating channel classes up to VoiceChannel

[bsian03]

Typings are now in a usable state and am happy for them to be reviewed only for any corrections needing to be made. I'm still working on a couple of details (e.g. implementing) and inconsistencies so please refrain from doing reviews on them until I'm finished with it

[bsian03]

Typings should be finalised apart from ordering alphabetically

[bsian03]

Opinions for the change made in Permission/PermissionOverwrite?

[bsian03]

Okay well I waited long enough for any reviews and none were made, so I'm just going to push ahead with this merge.