app: use material.Decorations on undecorated platforms

This patch implements a mechanism for customizing window
decorations.
If a window is configured with app.Decorated(true), then
the widget/material.Decorations are applied. On Wayland,
the option is automatically set when the server does not
provide window decorations.

Server side decorations are no longer requested.
The Decorated flag is set according to the
server's requests.

Wayland is now the default driver for UNIX platforms.

References: https://todo.sr.ht/~eliasnaur/gio/318
Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

app/os_wayland.c

@@ -6,6 +6,7 @@
 
 #include <wayland-client.h>
 #include "wayland_xdg_shell.h"
+#include "wayland_xdg_decoration.h"
 #include "wayland_text_input.h"
 #include "_cgo_export.h"
 
@@ -29,6 +30,10 @@ const struct xdg_toplevel_listener gio_xdg_toplevel_listener = {
 	.close = gio_onToplevelClose,
 };
 
+const struct zxdg_toplevel_decoration_v1_listener gio_zxdg_toplevel_decoration_v1_listener = {
+	.configure = gio_onToplevelDecorationConfigure,
+};
+
 static void xdg_wm_base_handle_ping(void *data, struct xdg_wm_base *wm, uint32_t serial) {
 	xdg_wm_base_pong(wm, serial);
 }