Add an enum for Nether Wart growth stages. Adds BUKKIT-1599

By: GJ <gjmcferrin@gmail.com>

paper-api/src/main/java/org/bukkit/NetherWartsState.java

@@ -0,0 +1,20 @@
+package org.bukkit;
+
+public enum NetherWartsState {
+    /**
+     * State when first seeded
+     */
+    SEEDED,
+    /**
+     * First growth stage
+     */
+    STAGE_ONE,
+    /**
+     * Second growth stage
+     */
+    STAGE_TWO,
+    /**
+     * Ready to harvest
+     */
+    RIPE;
+}