gmain: Add names to various GSources constructed in GLib

For the purposes of debugging, it is quite useful for every GSource to
have a name set. Ensure that any GSource we construct inside GLib has a
name set. For GSources which are then returned to the caller, this name
can then be overridden with something even more useful by the caller.

Since this data is only used for debugging, avoid doing any allocations
for it; just use static strings.

https://gitlab.gnome.org/GNOME/glib/issues/1175

gio/glocalfilemonitor.c

@@ -648,6 +648,8 @@ g_file_monitor_source_new (gpointer           instance,
   source = g_source_new (&source_funcs, sizeof (GFileMonitorSource));
   fms = (GFileMonitorSource *) source;
 
+  g_source_set_name (source, "GFileMonitorSource");
+
   g_mutex_init (&fms->lock);
   fms->instance = instance;
   fms->pending_changes = g_sequence_new (pending_change_free);