Make spellvamp more effective on ""AoE"" abilities by making it scale with target count

Spell vamp drops to 1/3 effectiveness on AoE spells, but a lot of AoE spells really only technically qualify as such. This value is balanced around not making REAL AoE too strong, like Anivia's ult or Morgana's pool, but spells like Lux Q or Sona Q take that value even though they can only hit a maximum of two targets.

Instead of just making all spells apply 1/3 spell vamp when they qualify as DoTs or AoE, make them instead apply decreasing spell vamp as target count increases. If a spell hits only a single target it could apply 75% spell vamp, still a reduced value, at 2 targets it could drop to 50%, and 3 or more drop to the 33% it currently uses. On pass-through shots or DoTs that hit targets at different times it could start at 66% on the first target hit and scale down to 33% on the last targets it hits in a similar way to how Sivir's Q damage scales down.