[Feature] Premium subscriptions (#2781)

* what a big commit lel, add app sub enums

* work

* ah yup lol

* `?`

* events 1

* typo

* `list` => `get` | remaining events

* add `RespondWithPremiumRequiredAsync` to interaction module base

src/Discord.Net.WebSocket/ClientState.cs

@@ -17,6 +17,7 @@ namespace Discord.WebSocket
         private readonly ConcurrentDictionary<ulong, SocketGlobalUser> _users;
         private readonly ConcurrentHashSet<ulong> _groupChannels;
         private readonly ConcurrentDictionary<ulong, SocketApplicationCommand> _commands;
+        private readonly ConcurrentDictionary<ulong, SocketEntitlement> _entitlements;
 
         internal IReadOnlyCollection<SocketChannel> Channels => _channels.ToReadOnlyCollection();
         internal IReadOnlyCollection<SocketDMChannel> DMChannels => _dmChannels.ToReadOnlyCollection();
@@ -24,6 +25,7 @@ namespace Discord.WebSocket
         internal IReadOnlyCollection<SocketGuild> Guilds => _guilds.ToReadOnlyCollection();
         internal IReadOnlyCollection<SocketGlobalUser> Users => _users.ToReadOnlyCollection();
         internal IReadOnlyCollection<SocketApplicationCommand> Commands => _commands.ToReadOnlyCollection();
+        internal IReadOnlyCollection<SocketEntitlement> Entitlements => _entitlements.ToReadOnlyCollection();
 
         internal IReadOnlyCollection<ISocketPrivateChannel> PrivateChannels =>
             _dmChannels.Select(x => x.Value as ISocketPrivateChannel).Concat(
@@ -40,6 +42,7 @@ namespace Discord.WebSocket
             _users = new ConcurrentDictionary<ulong, SocketGlobalUser>(ConcurrentHashSet.DefaultConcurrencyLevel, (int)(estimatedUsersCount * CollectionMultiplier));
             _groupChannels = new ConcurrentHashSet<ulong>(ConcurrentHashSet.DefaultConcurrencyLevel, (int)(10 * CollectionMultiplier));
             _commands = new ConcurrentDictionary<ulong, SocketApplicationCommand>();
+            _entitlements = new();
         }
 
         internal SocketChannel GetChannel(ulong id)
@@ -170,5 +173,29 @@ namespace Discord.WebSocket
             foreach (var id in ids)
                 _commands.TryRemove(id, out var _);
         }
+
+        internal void AddEntitlement(ulong id, SocketEntitlement entitlement)
+        {
+            _entitlements.TryAdd(id, entitlement);
+        }
+
+        internal SocketEntitlement GetEntitlement(ulong id)
+        {
+            if (_entitlements.TryGetValue(id, out var entitlement))
+                return entitlement;
+            return null;
+        }
+
+        internal SocketEntitlement GetOrAddEntitlement(ulong id, Func<ulong, SocketEntitlement> entitlementFactory)
+        {
+            return _entitlements.GetOrAdd(id, entitlementFactory);
+        }
+
+        internal SocketEntitlement RemoveEntitlement(ulong id)
+        {
+            if(_entitlements.TryRemove(id, out var entitlement))
+                return entitlement;
+            return null;
+        }
     }
 }