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/gdscript/gdscript.cpp

@@ -30,6 +30,7 @@
 
 #include "gdscript.h"
 
+#include "core/object/callable_mp.h"
 #include "core/object/class_db.h"
 #include "gdscript_analyzer.h"
 #include "gdscript_cache.h"