* Fix parser expanding dots where it shouldn't
Previously, the parser would expand "a...b" as "a../..b". Now, >2 dots
are only expanded when the whole path component consists of dots (i.e.,
"..." expands to "../.." while "a...b" stays as it is).
* Respect OS separator when expanding >2 dots
"..." now expands to either "../.." or "..\..", based on the host OS.
* refactor: expand_path and expand_ndots now work for any string.
* refactor: refactor test and add new ones.
* refactor: convert expanded to owned string
* feat: pub export of expand_ndots
* feat: add completion for ndots in fs-shell
* Expand n dots early where tilde was also expanded.
* Remove normalize, not needed.
New function absolutize, doesn't follow links neither checks existence.
Renamed canonicalize_existing to canonicalize, works as expected.
* Remove normalize usages, change canonicalize.
* Treat strings as paths
