* Use next and avoid a redundant prefix strip
* Avoid allocations
Especially when `expand_tilde` is claled on a path
that doesn't contain a tilde.
* Add a test
* Use Into<Cow<…>>
* Put the expand_tilde test at the end of the file
* Remove unused importsw
helix-stdx is meant to carry extensions to the stdlib or low-level
dependencies that are useful in all other crates. This commit starts
with all of the path functions from helix-core and the CWD tracking that
lived in helix-loader.
The CWD tracking in helix-loader was previously unable to call the
canonicalization functions in helix-core. Switching to our custom
canonicalization code should make no noticeable difference though
since `std::env::current_dir` returns a canonicalized path with
symlinks resolved (at least on unix).
