Add Granted OAuth2 Scopes to GUILD_CREATE event

[CanIGetaPR]

Since there is more than one possible OAuth2 scope for a bot in a guild, the GUILD_CREATE event should return an array of scopes the bot has been granted in this guild.

https://discord.com/developers/docs/topics/gateway#guild-create

Also Addresses:
#3792
#3341
#3656 (comment)
#2673