Add widget-drop-down for Air

src/widget-drop-down.h

@@ -0,0 +1,13 @@
+// SPDX-FileCopyrightText: 2023-2024 Geoffrey D. Bennett <g@b4.vu>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#pragma once
+
+#include <gtk/gtk.h>
+
+#include "alsa.h"
+
+GtkWidget *make_drop_down_alsa_elem(
+  struct alsa_elem *elem,
+  const char       *label_text
+);