Move logic from EvenHealthChangeEntityEffectSystem to the damage system API (#41684)

Move logic from EvenHealthChangeEntityEffectSystem to the damage system API (#41684)

* add two methods

* move stuff to damage system api

* use TryIndex

* simplify

* minor fix

* add helper functions

* fix

* remove random new line

* simplify

* remove unnecessary lines

* rename to GetDamage

* Got it working

* make more clear

* why backwards

* value should be the amount to heal

* fix

* fix all dumb fixedpoint2 edge cases I hope

* One more thing

* fix

* make it more simple

* ops it was backwards

* valueHeal can't be more than remaining

* add all keys beforehand and no need to check and add them inside the loop

* break for loop in case remaining is zero

* comment was wrong

* optimized, works

* remove random spaces

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Co-authored-by: Princess Cheeseballs <66055347+Pronana@users.noreply.github.com>