[Feature] Media channel support (#2725)

* initial commit

* oops

* another typo -_-

* Update AttachmentFlags.cs

Made this on my phone lol

* Update AttachmentFlags.cs

* -line

* initial impl

* some guild methods for media (and forum) channels

* file attachment can be a thumbnail

* can't edit media channel layout

* updatess

* Update ChannelPermissions.cs

* typo

src/Discord.Net.WebSocket/Entities/Guilds/SocketGuild.cs

@@ -339,6 +339,15 @@ namespace Discord.WebSocket
         public IReadOnlyCollection<SocketForumChannel> ForumChannels
             => Channels.OfType<SocketForumChannel>().ToImmutableArray();
 
+        /// <summary>
+        ///     Gets a collection of all media channels in this guild.
+        /// </summary>
+        /// <returns>
+        ///     A read-only collection of forum channels found within this guild.
+        /// </returns>
+        public IReadOnlyCollection<SocketMediaChannel> MediaChannels
+            => Channels.OfType<SocketMediaChannel>().ToImmutableArray();
+
         /// <summary>
         ///     Gets the current logged-in user.
         /// </summary>
@@ -790,6 +799,16 @@ namespace Discord.WebSocket
         public SocketCategoryChannel GetCategoryChannel(ulong id)
             => GetChannel(id) as SocketCategoryChannel;
 
+        /// <summary>
+        ///     Gets a media channel in this guild.
+        /// </summary>
+        /// <param name="id">The snowflake identifier for the stage channel.</param>
+        /// <returns>
+        ///     A stage channel associated with the specified <paramref name="id" />; <see langword="null"/> if none is found.
+        /// </returns>
+        public SocketMediaChannel GetMediaChannel(ulong id)
+            => GetChannel(id) as SocketMediaChannel;
+
         /// <summary>
         ///     Creates a new text channel in this guild.
         /// </summary>
@@ -857,7 +876,7 @@ namespace Discord.WebSocket
             => GuildHelper.CreateCategoryChannelAsync(this, Discord, name, options, func);
 
         /// <summary>
-        ///     Creates a new channel forum in this guild.
+        ///     Creates a new forum channel in this guild.
         /// </summary>
         /// <param name="name">The new name for the forum.</param>
         /// <param name="func">The delegate containing the properties to be applied to the channel upon its creation.</param>
@@ -870,6 +889,20 @@ namespace Discord.WebSocket
         public Task<RestForumChannel> CreateForumChannelAsync(string name, Action<ForumChannelProperties> func = null, RequestOptions options = null)
             => GuildHelper.CreateForumChannelAsync(this, Discord, name, options, func);
 
+        /// <summary>
+        ///     Creates a new media channel in this guild.
+        /// </summary>
+        /// <param name="name">The new name for the media channel.</param>
+        /// <param name="func">The delegate containing the properties to be applied to the channel upon its creation.</param>
+        /// <param name="options">The options to be used when sending the request.</param>
+        /// <exception cref="ArgumentNullException"><paramref name="name"/> is <see langword="null"/>.</exception>
+        /// <returns>
+        ///     A task that represents the asynchronous creation operation. The task result contains the newly created
+        ///     media channel.
+        /// </returns>
+        public Task<RestMediaChannel> CreateMediaChannelAsync(string name, Action<ForumChannelProperties> func = null, RequestOptions options = null)
+            => GuildHelper.CreateMediaChannelAsync(this, Discord, name, options, func);
+
         internal SocketGuildChannel AddChannel(ClientState state, ChannelModel model)
         {
             var channel = SocketGuildChannel.Create(this, state, model);
@@ -2075,6 +2108,21 @@ namespace Discord.WebSocket
         /// <inheritdoc />
         Task<ITextChannel> IGuild.GetPublicUpdatesChannelAsync(CacheMode mode, RequestOptions options)
             => Task.FromResult<ITextChannel>(PublicUpdatesChannel);
+
+        /// <inheritdoc />
+        Task<IForumChannel> IGuild.GetForumChannelAsync(ulong id, CacheMode mode, RequestOptions options)
+            => Task.FromResult<IForumChannel>(GetForumChannel(id));
+        /// <inheritdoc />
+        Task<IReadOnlyCollection<IForumChannel>> IGuild.GetForumChannelsAsync(CacheMode mode, RequestOptions options)
+            => Task.FromResult<IReadOnlyCollection<IForumChannel>>(ForumChannels);
+
+        /// <inheritdoc />
+        Task<IMediaChannel> IGuild.GetMediaChannelAsync(ulong id, CacheMode mode, RequestOptions options)
+            => Task.FromResult<IMediaChannel>(GetMediaChannel(id));
+        /// <inheritdoc />
+        Task<IReadOnlyCollection<IMediaChannel>> IGuild.GetMediaChannelsAsync(CacheMode mode, RequestOptions options)
+            => Task.FromResult<IReadOnlyCollection<IMediaChannel>>(MediaChannels);
+
         /// <inheritdoc />
         async Task<ITextChannel> IGuild.CreateTextChannelAsync(string name, Action<TextChannelProperties> func, RequestOptions options)
             => await CreateTextChannelAsync(name, func, options).ConfigureAwait(false);
@@ -2091,6 +2139,10 @@ namespace Discord.WebSocket
         async Task<IForumChannel> IGuild.CreateForumChannelAsync(string name, Action<ForumChannelProperties> func, RequestOptions options)
             => await CreateForumChannelAsync(name, func, options).ConfigureAwait(false);
 
+        /// <inheritdoc />
+        async Task<IMediaChannel> IGuild.CreateMediaChannelAsync(string name, Action<ForumChannelProperties> func, RequestOptions options)
+            => await CreateMediaChannelAsync(name, func, options).ConfigureAwait(false);
+
         /// <inheritdoc />
         async Task<IReadOnlyCollection<IVoiceRegion>> IGuild.GetVoiceRegionsAsync(RequestOptions options)
             => await GetVoiceRegionsAsync(options).ConfigureAwait(false);