`Modules`: Don't include headers in module declaration

```
[build] ../vulkan.cppm:64:10: warning: '#include ' attaches the declarations to the named module 'vulkan', which is not usually intended; consider moving that directive before the module declaration
```

I get this warning when building the vulkan module. I don't understand what was wrong with just specifying the exported types directly inside `cppm`, why does it need to go through the headers now.
To me it seems like the vulkan module implementation is getting worse and worse.

Start with vulkan.cppm around line 64 and reproduce the reported build warning to understand how the header include relates to the module declaration. Compare this with the earlier approach of specifying exported types directly in cppm; done means the module no longer emits the warning about attaching included declarations to the named module.

Written by the indexing model from the issue text.