Update socket presence and add new presence event (#1945)

src/Discord.Net.Core/Entities/Users/IPresence.cs

@@ -1,4 +1,4 @@
-using System.Collections.Immutable;
+using System.Collections.Generic;
 
 namespace Discord
 {
@@ -14,10 +14,10 @@ namespace Discord
         /// <summary>
         ///     Gets the set of clients where this user is currently active.
         /// </summary>
-        IImmutableSet<ClientType> ActiveClients { get; }
+        IReadOnlyCollection<ClientType> ActiveClients { get; }
         /// <summary>
         ///     Gets the list of activities that this user currently has available.
         /// </summary>
-        IImmutableList<IActivity> Activities { get; }
+        IReadOnlyCollection<IActivity> Activities { get; }
     }
 }