Godex crashes when closing the editor

[AndreaCatania]

The crash is caused because the ScriptInstances inside ScriptEcs are cleared when the function unregister_modules_types is execute https://github.com/GodotECS/godex/blob/main/modules/godot/register_types.cpp#L156

However, at that time the scripts are already cleared out, and this cause a segmentation fault when the function _predelete is executed.

To fix this issue, it's necessary to clear the ScriptECS during the cleanup. This godot PR introduces a mechanism to get such callback: godotengine/godot#50179.