Add EntityPushByExplodeEvent

[yoyosource]

Add a way to check what Entity got pushed by an Explosion happening. This event is only called for non LivingEntities because there is the EntityKnockbackEvent for that already. I am using this on a server where I am a Developer already for cancelling specific Explosions knocking around other Entities.

[lynxplay]

We already have EntityKnockbackEvent and EntityKnockbackByAttackEvent which both are fine with plain entities.

The event you are proposing is pretty much a 1 to 1 copy of EntityPushedByEntityAttackEvent.
I think the solution here is to call the previously mentioned events.
Change org.bukkit.craftbukkit.event.CraftEventFactory#callEntityKnockbackEvent to take in an CraftEntity instead of CraftLivingEntity and then call the correct legacy and paper events if the entity is living vs not.

[Huge-mistake]

Yo, is this PR ready? Seems like it could fix the issue. @lynxplay
#13326

[yoyosource]

I have tested it and locally it works. I am just waiting on a second review from somebody or the first reviewer.

[Huge-mistake]

https://github.com/yoyosource/Paper/blob/feature/EntityPushByExplodeEvent/paper-server/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java#L2074

May trigger NPE and requires a minor modification.
event.setCancelled(legacyEvent != null && legacyEvent.isCancelled());

[yoyosource]

Good catch. I will fix it later.