Fix bonus multiplier issue in rP22754 (multiple attack effects) and consider more entities in EntitiesNearPoint
- the bonus multiplier would self-multiply with every effect, so an attack with multiple effect would have a broken multiplier.
- EntitiesNearPoint used IID_Resistance, which is now facultative. To not miss entities, it now returns all entities owned by enemy players. For GAIA it checks for Health to avoid returning trees.
This means enemy units have higher priority over missed projectiles, but that should generally be OK.
This also adds simple tests.
Reported By: Freagarach
Differential Revision: https://code.wildfiregames.com/D2322