tests: Add test running basic perf test

This test runs all of GNOME Shell using the headless backend inside a
mocked D-Bus environment. The basic test tests, well, basic things, like
the panel menu, the overview, showing the app grid view, as well as
going back to the session view.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1349>

data/meson.build

@@ -1,3 +1,5 @@
+data_builddir = meson.current_build_dir()
+
 desktop_files = [
   'org.gnome.Shell.desktop',
   'org.gnome.Shell.Extensions.desktop',
@@ -134,5 +136,5 @@ endif
 custom_target('compile-schemas',
   input: schema,
   output: 'gschemas.compiled',
-  command: [find_program('glib-compile-schemas'), meson.current_build_dir()],
+  command: [find_program('glib-compile-schemas'), data_builddir],
   build_by_default: true)