SPIGOT-4526: Add conversion time API for Zombie & subclasses

By: md_5 <git@md-5.net>

paper-api/src/main/java/org/bukkit/entity/Zombie.java

@@ -48,4 +48,35 @@ public interface Zombie extends Monster {
      */
     @Deprecated
     public Villager.Profession getVillagerProfession();
+
+    /**
+     * Get if this entity is in the process of converting to a Drowned as a
+     * result of being underwater.
+     *
+     * @return conversion status
+     */
+    boolean isConverting();
+
+    /**
+     * Gets the amount of ticks until this entity will be converted to a Drowned
+     * as a result of being underwater.
+     *
+     * When this reaches 0, the entity will be converted.
+     *
+     * @return conversion time
+     * @throws IllegalStateException if {@link #isConverting()} is false.
+     */
+    int getConversionTime();
+
+    /**
+     * Sets the amount of ticks until this entity will be converted to a Drowned
+     * as a result of being underwater.
+     *
+     * When this reaches 0, the entity will be converted. A value of less than 0
+     * will stop the current conversion process without converting the current
+     * entity.
+     *
+     * @param time new conversion time
+     */
+    void setConversionTime(int time);
 }