Add support for entity final damage callbacks

[Dinorush]

Adds FinalDamageCallbacks to entities.

Final damage callbacks exist for classes and are only used for multiplicative changes to damage to avoid issues where a later damage callback adds/subtracts a flat amount. This is why, for instance, Sword Block uses a final damage callback, as otherwise Railgun's charge damage ignores the damage reduction (as the Railgun callback is added after). Entities don't have these callbacks currently.

Primarily adding this to support better Frontier War harvester damage callback code, but usable elsewhere.

[NoCatt]

Code looks good, worked in testing, adding as well as removing callbacks,

[uniboi]

Tested by adding and removing FinalDamageCallbacks to an entity and killing it in game.
Works in testing and the code looks good as well

[GeckoEidechse]

@NoCatt @uniboi did you test backwards compat as well? If not I can do it. Just wanna double check so I don't accidentally make a breaking release by accident ^^"

[NoCatt]

@NoCatt @uniboi did you test backwards compat as well? If not I can do it. Just wanna double check so I don't accidentally make a breaking release by accident ^^"

Since its server only, there is no reason it should cause any issues with clients on old versions

[GeckoEidechse]

I did not test / code review PR, simply giving sign-off approval based on other reviews.