feat: add bukkit class type

Signed-off-by: MiaoWoo <admin@yumc.pw>

packages/bukkit/src/typings/org.bukkit.UndefinedNullability.ts

@@ -0,0 +1,11 @@
+declare namespace org {
+    namespace bukkit {
+        class UndefinedNullability {
+            /**
+             * Human readable description of the circumstances, in which the type is
+             * nullable.
+             */
+            public value(): string;
+        }
+    }
+}