Core/Auras: Convert most rules from Aura::CanBeSaved to a custom spell attribute

Port From (https://github.com/TrinityCore/TrinityCore/commit/b4aa698acb88e1a74bc22d97279148a567b88cad)

Source/Game/Spells/Auras/Aura.cs

@@ -957,49 +957,7 @@ namespace Game.Spells
                 if (GetSpellInfo().IsSingleTarget())
                     return false;
 
-            // No point in saving this, since the stable dialog can't be open on aura load anyway.
-            if (HasEffectType(AuraType.OpenStable))
-                return false;
-
-            // Can't save vehicle auras, it requires both caster & target to be in world
-            if (HasEffectType(AuraType.ControlVehicle))
-                return false;
-
-            // do not save bind sight auras
-            if (HasEffectType(AuraType.BindSight))
-                return false;
-
-            // no charming auras (taking direct control)
-            if (HasEffectType(AuraType.ModPossess) || HasEffectType(AuraType.ModPossessPet))
-                return false;
-
-            // no charming auras can be saved
-            if (HasEffectType(AuraType.ModCharm) || HasEffectType(AuraType.AoeCharm))
-                return false;
-
-            // no battleground player positions
-            if (HasEffectType(AuraType.BattleGroundPlayerPosition) || HasEffectType(AuraType.BattleGroundPlayerPositionFactional))
-                return false;
-
-            // Incanter's Absorbtion - considering the minimal duration and problems with aura stacking
-            // we skip saving this aura
-            // Also for some reason other auras put as MultiSlot crash core on keeping them after restart,
-            // so put here only these for which you are sure they get removed
-            switch (GetId())
-            {
-                case 44413: // Incanter's Absorption
-                case 40075: // Fel Flak Fire
-                case 55849: // Power Spark
-                    return false;
-            }
-
-            // When a druid logins, he doesnt have either eclipse power, nor the marker auras, nor the eclipse buffs. Dont save them.
-            if (GetId() == 67483 || GetId() == 67484 || GetId() == 48517 || GetId() == 48518)
-                return false;
-
-            // Don't save druid forms, only the dummy. It will cast the appropriate form
-            //        Swift Flight            Flight             Aquatic                Stag
-            if (GetId() == 40120 || GetId() == 33943 || GetId() == 1066 || GetId() == 165961)
+            if (GetSpellInfo().HasAttribute(SpellCustomAttributes.AuraCannotBeSaved))
                 return false;
 
             // don't save auras removed by proc system