tests/cursor: Embed a copy of the Adwaita cursor theme

As a follow-up to 87cc6633a5, embed a partial copy of the Adwaita cursor theme
and point to it with XCURSOR_PATH to make the test completely independent
from the installed cursor themes.

Indeed, adwaita-icon-theme changed ever so slightly in version 48 so the
ref tests started failing when the new version was installed.

This is a copy of adwaita-icon-theme 47, which is what was used to generate
the ref images.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4252>

src/tests/cursor-tests.c

@@ -672,6 +672,7 @@ main (int    argc,
       char **argv)
 {
   g_autoptr (MetaContext) context = NULL;
+  g_autofree char *path = NULL;
 
   context = meta_create_test_context (META_CONTEXT_TEST_TYPE_TEST,
                                       (META_CONTEXT_TEST_FLAG_NO_X11 |
@@ -681,6 +682,9 @@ main (int    argc,
   meta_context_test_set_background_color (META_CONTEXT_TEST (context),
                                           COGL_COLOR_INIT (255, 255, 255, 255));
 
+  path = g_test_build_filename (G_TEST_DIST, "tests", "xcursors", NULL);
+  g_setenv ("XCURSOR_PATH", path, TRUE);
+
   test_context = context;
 
   init_tests ();

src/tests/meson.build

@@ -1091,6 +1091,7 @@ if have_installed_tests
   install_subdir('migration', install_dir: tests_datadir)
   install_subdir('ref-tests', install_dir: tests_datadir)
   install_subdir('icc-profiles', install_dir: tests_datadir)
+  install_subdir('xcursors', install_dir: tests_datadir)
 
   install_data('org.gnome.mutter.test.gschema.xml', install_dir: tests_datadir)
 

src/tests/wayland-test-clients/cursor-tests-client.c

@@ -127,7 +127,7 @@ on_pointer_enter (WaylandSurface    *surface,
            "and actual scale %f",
            effective_theme_size, theme_size, scale);
 
-  cursor_theme = wl_cursor_theme_load ("Adwaita",
+  cursor_theme = wl_cursor_theme_load (NULL,
                                        effective_theme_size,
                                        display->shm);
   cursor = wl_cursor_theme_get_cursor (cursor_theme, cursor_name);