OverKillDamage
Tracking Issue: #805
The UnitState's damage results array only holds the actual damage taken by the unit, so the result can't be higher than the unit's HP.
This adds the OverkillDamage Unit value, which is shows how higher the kill damage value was from the standard Unit HP.
One of its use cases is to modify the effects of the abilities that trigger on death, like the trigger chance on Advent Priest's Sustain.
The OverKillDamage calculated by XCGS_Unit is negative, but the unit value is set to be positive to make using it more intuitive.
The value uses eCleanup_BeginTactical.