Add a utility for generating a Windows application manifest

[segevfiner]

Instead of having to hand code a Windows application manifest and embed it into the build.rs script as a string or as a file, it would be nice to have a utility to generate such a manifest by code. e.g.

    shadow.set_manifest(WindowsManifest::new()
        .set_...()
        .set_...()
        .build())

See https://learn.microsoft.com/en-us/windows/win32/sbscs/application-manifests