Core/Spells: Implement spell queue

Port From (https://github.com/TrinityCore/TrinityCore/commit/27019a62a4294f8dd48d975f85b1907c5adee0e3)

Source/Game/Entities/Player/Player.cs

@@ -358,6 +358,10 @@ namespace Game.Entities
             base.Update(diff);
             SetCanDelayTeleport(false);
 
+            // Unit::Update updates the spell history and spell states. We can now check if we can launch another pending cast.
+            if (CanExecutePendingSpellCastRequest())
+                ExecutePendingSpellCastRequest();
+
             long now = GameTime.GetGameTime();
 
             UpdatePvPFlag(now);
@@ -642,6 +646,9 @@ namespace Game.Entities
                     return;
                 }
 
+                // clear all pending spell cast requests when dying
+                CancelPendingCastRequest();
+
                 // drunken state is cleared on death
                 SetDrunkValue(0);