[Bleeding] Repair missing diff in Explosion. Fixes BUKKIT-5662

The blast protection enchantment dampers explosions, however
the functionality was only added to block explosions, and not
entity explosions.
[Bleeding] Implement new damage api. Fixes BUKKIT-5326, BUKKIT-3878.

This commit centralizes event handling to where damage is actually applied
to the entity to avoid bugs that have resulted from nodamageticks,
modifications to damage after the event has been called, and similar
mishaps. This also implements new API for getting and setting of
modifications made to the damage amount actually applied to the entity.
This is done by storing the change in the damage amount as each modifier
is applied by vanilla code.

The method that actually damages the armor worn by an entity has been
relocated beneath the event called as to not apply durability loss when
the event has been cancelled.
[Bleeding] Set projectile source for reflected fireballs. Fixes BUKKIT-5661