types(DropdownItem): add DropdownItemInstance type (#9214)

src/dropdown-menu/types.ts

@@ -0,0 +1,9 @@
+import type { Ref } from 'vue';
+import type { DropdownMenuProps } from './DropdownMenu';
+
+export type DropdownMenuDirection = 'up' | 'down';
+
+export type DropdownMenuProvide = {
+  props: DropdownMenuProps;
+  offset: Ref<number>;
+};