9836: Refactor: quick clean-up of iteration idioms in the `vfs` crate r=matklad a=Some-Dood
This PR cleans up some of the iteration idioms used in the `vfs` crate. Most of the changes simply converted `for` loops into their `std::iter::Iterator`-method counterpart. Other changes required some inversion of logic to accommodate for better short-circuiting. Overall, there should be no behavioral changes. If there are any stylistic issues, I will gladly adhere to them and adjust the PR accordingly. Thanks!
Co-authored-by: Basti Ortiz <39114273+Some-Dood@users.noreply.github.com>