refactor recursive deletion into a struct maintaining the dir stack

it can remove arbitrarily-deep directory trees without exhausting
the stack or file descriptor limits.
The symlink attack/TOCTOU from CVE-2022-21658 that can occur when
traversing the directory hierarchy more than level at a time is
addressed by retracing the .. hierarchy after opening a descendant.
Opening .. isn't subject to symlink attacks so we can reliably compare
dev/ino numbers.

Author: the8472

library/std/src/lib.rs

@@ -296,6 +296,7 @@
 #![feature(int_roundings)]
 #![feature(ip)]
 #![feature(ip_in_core)]
+#![feature(iter_advance_by)]
 #![feature(maybe_uninit_slice)]
 #![feature(maybe_uninit_uninit_array)]
 #![feature(maybe_uninit_write_slice)]