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`.

scene/debugger/runtime_node_select.cpp

@@ -39,6 +39,7 @@
 #include "core/input/input.h"
 #include "core/input/input_event.h"
 #include "core/math/geometry_3d.h"
+#include "core/object/callable_mp.h"
 #include "scene/2d/camera_2d.h"
 #include "scene/debugger/scene_debugger_object.h"
 #include "scene/gui/popup_menu.h"