Add a hook for CustomPlayer to overwrite behavior when an enemy applies negative buff

[herbix]

Monsters like Lagavulin or Spire Shield can apply negative buff to player. But for some mod characters, strength or dexterity doesn't make them powerful. This makes the specific monster action useless and weakens the monster. This hook makes it possible for mod makers to overwrite the power to be applied to player by these monsters, just like Spire Shield can apply negative focus in some cases. But they can use their own power.