feat(widget): add dropdown widget as pick_list replacement

The Dropdown widget is based on the PickList widget from iced.

src/widget/dropdown/mod.rs

@@ -0,0 +1,17 @@
+// Copyright 2023 System76 <info@system76.com>
+// Copyright 2019 Héctor Ramón, Iced contributors
+// SPDX-License-Identifier: MPL-2.0 AND MIT
+
+pub mod menu;
+pub use menu::Menu;
+
+mod widget;
+pub use widget::*;
+
+pub fn dropdown<'a, S: AsRef<str>, Message: 'a>(
+    selections: &'a [S],
+    selected: Option<usize>,
+    on_selected: impl Fn(usize) -> Message + 'a,
+) -> Dropdown<'a, S, Message> {
+    Dropdown::new(selections, selected, on_selected)
+}