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`.

editor/plugins/editor_plugin.cpp

@@ -31,6 +31,7 @@
 #include "editor_plugin.h"
 #include "editor_plugin.compat.inc"
 
+#include "core/object/callable_mp.h"
 #include "core/object/class_db.h"
 #include "editor/debugger/editor_debugger_node.h"
 #include "editor/debugger/editor_debugger_plugin.h"

editor/plugins/editor_plugin_settings.cpp

@@ -35,6 +35,7 @@
 #include "core/io/config_file.h"
 #include "core/io/dir_access.h"
 #include "core/io/file_access.h"
+#include "core/object/callable_mp.h"
 #include "editor/editor_node.h"
 #include "editor/editor_string_names.h"
 #include "editor/themes/editor_scale.h"

editor/plugins/plugin_config_dialog.cpp

@@ -32,6 +32,7 @@
 
 #include "core/io/config_file.h"
 #include "core/io/dir_access.h"
+#include "core/object/callable_mp.h"
 #include "core/object/class_db.h"
 #include "core/object/script_language.h"
 #include "editor/editor_node.h"