feature: Add GuildUser IsPending property (#1731)

* Implemented Pending property

* Implemented changes

src/Discord.Net.WebSocket/Entities/Users/SocketGuildUser.cs

@@ -57,6 +57,8 @@ namespace Discord.WebSocket
         /// <inheritdoc />
         public bool IsStreaming => VoiceState?.IsStreaming ?? false;
         /// <inheritdoc />
+        public bool? IsPending { get; private set; }
+        /// <inheritdoc />
         public DateTimeOffset? JoinedAt => DateTimeUtils.FromTicks(_joinedAtTicks);
         /// <summary>
         ///     Returns a collection of roles that the user possesses.
@@ -142,6 +144,8 @@ namespace Discord.WebSocket
                 UpdateRoles(model.Roles.Value);
             if (model.PremiumSince.IsSpecified)
                 _premiumSinceTicks = model.PremiumSince.Value?.UtcTicks;
+            if (model.Pending.IsSpecified)
+                IsPending = model.Pending.Value;
         }
         internal void Update(ClientState state, PresenceModel model, bool updatePresence)
         {

src/Discord.Net.WebSocket/Entities/Users/SocketWebhookUser.cs

@@ -65,6 +65,8 @@ namespace Discord.WebSocket
         /// <inheritdoc />
         DateTimeOffset? IGuildUser.PremiumSince => null;
         /// <inheritdoc />
+        bool? IGuildUser.IsPending => null;
+        /// <inheritdoc />
         GuildPermissions IGuildUser.GuildPermissions => GuildPermissions.Webhook;
 
         /// <inheritdoc />