Move MetaProfiler from the backend to core

It's not really a backend thing, and we'll want to profile e.g. loading
the backend too, so create it very early and destroy it very late and
let MetaContextMain own it.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2678>

src/backends/meta-backend.c

@@ -74,10 +74,6 @@
 #include "meta/meta-enum-types.h"
 #include "meta/util.h"
 
-#ifdef HAVE_PROFILER
-#include "backends/meta-profiler.h"
-#endif
-
 #ifdef HAVE_REMOTE_DESKTOP
 #include "backends/meta-dbus-session-watcher.h"
 #include "backends/meta-remote-access-controller-private.h"
@@ -158,10 +154,6 @@ struct _MetaBackendPrivate
   MetaRemoteDesktop *remote_desktop;
 #endif
 
-#ifdef HAVE_PROFILER
-  MetaProfiler *profiler;
-#endif
-
 #ifdef HAVE_LIBWACOM
   WacomDeviceDatabase *wacom_db;
 #endif
@@ -262,10 +254,6 @@ meta_backend_dispose (GObject *object)
 
   g_clear_object (&priv->settings);
 
-#ifdef HAVE_PROFILER
-  g_clear_object (&priv->profiler);
-#endif
-
   g_clear_pointer (&priv->default_seat, clutter_seat_destroy);
   g_clear_pointer (&priv->stage, clutter_actor_destroy);
   g_clear_pointer (&priv->idle_manager, meta_idle_manager_free);
@@ -1220,10 +1208,6 @@ meta_backend_initable_init (GInitable     *initable,
              system_bus_gotten_cb,
              backend);
 
-#ifdef HAVE_PROFILER
-  priv->profiler = meta_profiler_new ();
-#endif
-
   if (!init_clutter (backend, error))
     return FALSE;