Add entity knockback events

- EntityKnockbackEvent
- EntityPushedByEntityAttackEvent
- EntityKnockbackByEntityEvent

Co-authored-by: aerulion <aerulion@gmail.com>
Co-authored-by: Jake Potrebic <jake.m.potrebic@gmail.com>

paper-server/patches/sources/net/minecraft/world/entity/boss/enderdragon/EnderDragon.java.patch

@@ -81,6 +81,15 @@
              }
          }
  
+@@ -417,7 +441,7 @@
+                 double d3 = entity.getZ() - d1;
+                 double d4 = Math.max(d2 * d2 + d3 * d3, 0.1D);
+ 
+-                entity.push(d2 / d4 * 4.0D, 0.20000000298023224D, d3 / d4 * 4.0D);
++                entity.push(d2 / d4 * 4.0D, 0.20000000298023224D, d3 / d4 * 4.0D, this); // Paper - Add EntityKnockbackByEntityEvent and EntityPushedByEntityAttackEvent
+                 if (!this.phaseManager.getCurrentPhase().isSitting() && entityliving.getLastHurtByMobTimestamp() < entity.tickCount - 2) {
+                     DamageSource damagesource = this.damageSources().mobAttack(this);
+ 
 @@ -458,6 +482,9 @@
          int j1 = Mth.floor(box.maxZ);
          boolean flag = false;