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`.

tests/core/variant/test_array.cpp

@@ -32,7 +32,7 @@
 
 TEST_FORCE_LINK(test_array)
 
-#include "core/object/callable_method_pointer.h"
+#include "core/object/callable_mp.h"
 #include "core/variant/array.h"
 #include "core/variant/typed_array.h"
 #include "tests/test_tools.h"