[FActiveGameplayEffect](API\Plugins\GameplayAbilities\FActiveGameplayEffect) * ApplyGameplayEffectSpec ( const [FGameplayEffectSpec](API\Plugins\GameplayAbilities\FGameplayEffectSpec) & Spec, [FPredictionKey](API\Plugins\GameplayAbilities\FPredictionKey) & InPredictionKey, bool & bFoundExistingStackableGE )