app: implement Window.Close for Wayland

This is a followup from a question sent to the mailing list.

Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

app/os_wayland.go

@@ -1478,8 +1478,10 @@ func (w *window) ShowTextInput(show bool) {}
 
 func (w *window) SetInputHint(_ key.InputHint) {}
 
-// Close the window. Not implemented for Wayland.
-func (w *window) Close() {}
+// Close the window.
+func (w *window) Close() {
+	w.dead = true
+}
 
 // Maximize the window. Not implemented for Wayland.
 func (w *window) Maximize() {}

app/window.go

@@ -303,7 +303,7 @@ func (w *Window) SetCursorName(name pointer.CursorName) {
 // Close the window. The window's event loop should exit when it receives
 // system.DestroyEvent.
 //
-// Currently, only macOS, Windows and X11 drivers implement this functionality,
+// Currently, only macOS, Windows, X11 and Wayland drivers implement this functionality,
 // all others are stubbed.
 func (w *Window) Close() {
 	w.driverDefer(func(d driver) {