[Feature] Add missing VoiceChannel properties (#2573)

* add missing properties

* forgot about `MockedVoiceChannel`

src/Discord.Net.Rest/Entities/Guilds/GuildHelper.cs

@@ -285,6 +285,8 @@ namespace Discord.Rest
                         Deny = overwrite.Permissions.DenyValue.ToString()
                     }).ToArray()
                     : Optional.Create<API.Overwrite[]>(),
+                VideoQuality = props.VideoQualityMode,
+                RtcRegion = props.RTCRegion
             };
             var model = await client.ApiClient.CreateGuildChannelAsync(guild.Id, args, options).ConfigureAwait(false);
             return RestVoiceChannel.Create(client, guild, model);