Allow free() to be used as Callable

This method is registered in a special way so ClassDB doesn't naturally
know about its existence. Here it is hardcoded if any other option fail
to check if it is about the `free()` method and, if so, say it exists
and return a Callable.

core/object/class_db.cpp

@@ -31,6 +31,7 @@
 #include "class_db.h"
 
 #include "core/config/engine.h"
+#include "core/core_string_names.h"
 #include "core/io/resource_loader.h"
 #include "core/object/script_language.h"
 #include "core/os/mutex.h"
@@ -1299,6 +1300,12 @@ bool ClassDB::get_property(Object *p_object, const StringName &p_property, Varia
 		check = check->inherits_ptr;
 	}
 
+	// The "free()" method is special, so we assume it exists and return a Callable.
+	if (p_property == CoreStringNames::get_singleton()->_free) {
+		r_value = Callable(p_object, p_property);
+		return true;
+	}
+
 	return false;
 }