correctly handle opening helix inside symlinked directory

[pascalkuthe]

get_current_directory alnways returns a cannonicalized path (since cwd is just a file descriptor that is passed to realpath). That means that opening any file inside a symlinked directory would show that file as an absolute path outised the cwd instead of as an relative path (since we don't cannonicalize/resolve symlinks normally). To fix that I made helix mirror the behavior of pwd -L. We use PWD environment variable set by the shell which has a "memory" of which symlinks were transversed with cd.