xwayland: Add API to send signal to the Xwayland process

Will be used for test cases to fake-crash the Xwayland process.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2364>

src/wayland/meta-xwayland.c

@@ -1276,3 +1276,19 @@ meta_xwayland_handle_xevent (XEvent *event)
 
   return FALSE;
 }
+
+gboolean
+meta_xwayland_signal (MetaXWaylandManager  *manager,
+                      int                   signum,
+                      GError              **error)
+{
+  if (!manager->proc)
+    {
+      g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                   "Can't send signal, Xwayland not running");
+      return FALSE;
+    }
+
+  g_subprocess_send_signal (manager->proc, signum);
+  return TRUE;
+}

src/wayland/meta-xwayland.h

@@ -50,4 +50,9 @@ void
 meta_xwayland_associate_window_with_surface (MetaWindow          *window,
                                              MetaWaylandSurface  *surface);
 
+META_EXPORT_TEST
+gboolean meta_xwayland_signal (MetaXWaylandManager  *manager,
+                               int                   signum,
+                               GError              **error);
+
 #endif /* META_XWAYLAND_H */