url: return backslashes from fileURLToPath on win

PR-URL: https://github.com/nodejs/node/pull/25349
Fixes: https://github.com/nodejs/node/issues/25265


Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Bartosz Sosnowski <bartosz@janeasystems.com>
Reviewed-By: John-David Dalton <john.david.dalton@gmail.com>