Add Beacon BlockState for hopper events. Fixes BUKKIT-3932

By: Travis Watkins <amaranth@ubuntu.com>

paper-api/src/main/java/org/bukkit/block/Beacon.java

@@ -0,0 +1,9 @@
+package org.bukkit.block;
+
+import org.bukkit.inventory.InventoryHolder;
+
+/**
+ * Represents a beacon.
+ */
+public interface Beacon extends BlockState, InventoryHolder {
+}