feature: Add GuildUser IsPending property (#1731)

* Implemented Pending property

* Implemented changes

src/Discord.Net.Rest/API/Common/GuildMember.cs

@@ -18,6 +18,8 @@ namespace Discord.API
         public Optional<bool> Deaf { get; set; }
         [JsonProperty("mute")]
         public Optional<bool> Mute { get; set; }
+        [JsonProperty("pending")]
+        public Optional<bool> Pending { get; set; }
         [JsonProperty("premium_since")]
         public Optional<DateTimeOffset?> PremiumSince { get; set; }
     }

src/Discord.Net.Rest/Entities/Users/RestGuildUser.cs

@@ -29,6 +29,8 @@ namespace Discord.Rest
         public DateTimeOffset? PremiumSince => DateTimeUtils.FromTicks(_premiumSinceTicks);
         /// <inheritdoc />
         public ulong GuildId => Guild.Id;
+        /// <inheritdoc />
+        public bool? IsPending { get; private set; }
 
         /// <inheritdoc />
         /// <exception cref="InvalidOperationException" accessor="get">Resolving permissions requires the parent guild to be downloaded.</exception>
@@ -73,6 +75,8 @@ namespace Discord.Rest
                 UpdateRoles(model.Roles.Value);
             if (model.PremiumSince.IsSpecified)
                 _premiumSinceTicks = model.PremiumSince.Value?.UtcTicks;
+            if (model.Pending.IsSpecified)
+                IsPending = model.Pending.Value;
         }
         private void UpdateRoles(ulong[] roleIds)
         {

src/Discord.Net.Rest/Entities/Users/RestWebhookUser.cs

@@ -52,6 +52,8 @@ namespace Discord.Rest
         /// <inheritdoc />
         string IGuildUser.Nickname => null;
         /// <inheritdoc />
+        bool? IGuildUser.IsPending => null;
+        /// <inheritdoc />
         GuildPermissions IGuildUser.GuildPermissions => GuildPermissions.Webhook;
 
         /// <inheritdoc />