IS_MOUNT is filepath a mount path

Examples:

Windows: is_mount("c:") false; is_mount("C:\") true
Linux, macOS, Windows: is_mount("/") true

function y = is_mount(filepath, backend)
arguments
  filepath {mustBeTextScalar}
  backend (1,:) string = ["python", "sys"]
end

fun = hbackend(backend, "is_mount");
y = fun(filepath);

end