[Search directory] Append / instead of prepending ./ for quick cd

[PatrickF1]

I decided appending / is a better, cleaner solution for quick cd than appending ./

• since prepending ./ is causing issues when the path starts with . or /, why not just append /? fd never appends / to its output so this is safe to do (see Display directories with trailing slashes sharkdp/fd#436)
• of course, we can't just append / to everything; we need to test if the path is actually a directory, but since we only do this when there's one path selected, it's not performance hindering
• a / at the end of only directories is cleaner, more natural, and has a more comprehensible than prepending ./ to anything even when it's not needed
• the code and documentation become much more straightforward
• this will remove support for executables, which cuts back on product debt
• fixes Auto prepend ./ for quick directory change doesn't work if directory starts with . #171 (is compatible with hidden directories)

This is about the same as the PR that started this all (#72) except we're using a trailing / instead.

Do note that symlink behavior changes if the directory has a trailing / (#185 (comment)).

[kidonng]

Also read the original PR for why I changed my mind to prepend ./ instead of appending /.

More examples of appending / changing other program's behavior (seems to only affect symlinks though):

~                                                                                                             
❯ command ls -l .nix-profile
lrwxr-xr-x  1 kid  staff  42 Jun 15 17:39 .nix-profile -> /nix/var/nix/profiles/per-user/kid/profile

~                                                                                                             
❯ command ls -l .nix-profile/
lrwxr-xr-x  1 kid  staff  16 Jul  4 14:04 .nix-profile/ -> profile-116-link

~                                                                                                             
❯ exa -l .nix-profile
dr-xr-xr-x  - kid  1 Jan  1970 bin
dr-xr-xr-x  - kid  1 Jan  1970 etc
lrwxr-xr-x 69 kid  1 Jan  1970 include -> /nix/store/kc4y8h2zf62adzyf9jsbpsfzlq4cpvyb-home-manager-path/include
dr-xr-xr-x  - kid  1 Jan  1970 lib
dr-xr-xr-x  - kid  1 Jan  1970 libexec
lrwxr-xr-x 62 kid  1 Jan  1970 Library -> /nix/store/mingfa89931g313929ixmr7wzcxjkyi3-nix-2.3.12/Library
lrwxr-xr-x 66 kid  1 Jan  1970 sbin -> /nix/store/kc4y8h2zf62adzyf9jsbpsfzlq4cpvyb-home-manager-path/sbin
dr-xr-xr-x  - kid  1 Jan  1970 share
lrwxr-xr-x 60 kid  1 Jan  1970 manifest.nix -> /nix/store/4iydni7d2f0dq9by6g1m9dz7xb34xdsr-env-manifest.nix

~                                                                                                             
❯ exa -l .nix-profile/
lrwxr-xr-x 16 kid  4 Jul 14:04 .nix-profile -> profile-116-link

~                                                                                                             
❯ command stat .nix-profile
16777220 12884994046 lrwxr-xr-x 1 kid staff 0 42 "Jun 15 17:39:05 2021" "Jun 15 17:39:05 2021" "Jun 15 17:39:05 2021" "Jun 15 17:39:05 2021" 4096 0 0 .nix-profile

~                                                                                                             
❯ command stat .nix-profile/
16777226 2189825 lrwxr-xr-x 1 kid staff 0 16 "Jul  4 14:04:01 2021" "Jul  4 14:04:01 2021" "Jul  4 14:04:01 2021" "Jul  4 14:04:01 2021" 4096 0 0 .nix-profile/

[PatrickF1]

Also read the original PR for why I changed my mind to prepend ./ instead of appending /.

Thanks. I replied in #171. Let's keep the discussion there.