Rename callable_method_pointer.h to callable_mp.h and include it explicitly

This allows removing it from `class_db.h`, significantly reducing the amount of files
that include it transitively.

Also includes some include cleanup in `control.h` and `rich_text_label.h` done while
ensure they don't depend on `callable_mp`.

modules/gridmap/editor/grid_map_editor_plugin.cpp

@@ -32,6 +32,7 @@
 
 #include "core/input/input.h"
 #include "core/math/geometry_2d.h"
+#include "core/object/callable_mp.h"
 #include "core/object/class_db.h"
 #include "core/os/keyboard.h"
 #include "editor/docks/editor_dock_manager.h"