app: add code for macOS and Windows apps under 'app' (#12933)

* app: add code for macOS and Windows apps under 'app'

* app: add readme

* app: windows and linux only for now

* ci: fix ui CI validation

---------

Co-authored-by: jmorganca <jmorganca@gmail.com>

app/cmd/app/menu.h

@@ -0,0 +1,27 @@
+#ifndef MENU_H
+#define MENU_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct
+{
+    char *label;
+    int enabled;
+    int separator;
+} menuItem;
+
+// TODO (jmorganca): these need to be forward declared in the webview.h file
+// for now but ideally they should be in this header file on windows too
+#ifndef WIN32
+int menu_get_item_count();
+void *menu_get_items();
+void menu_handle_selection(char *item);
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif