linux/bin/code.sh: use command -v instead of which

[jplatte]

command is a bash-builtin (see the Bash manual) that is guaranteed to always be present, in contrast to which, which is not required to be available for bash to work.

This dependency on which has recently caused an issue for a small percentage of arch linux users where VSCode wouldn't start anymore, see visual-studio-code-bin on the AUR. By removing the dependency, VSCode becomes a tiny bit more self-contained (unless it's still used somewhere else of course).

[Tyriar]

Good suggestion 👍

[eli-schwartz]

More generally, see https://unix.stackexchange.com/questions/85249/why-not-use-which-what-to-use-then
See also https://mywiki.wooledge.org/BashFAQ/081

command -v is guaranteed to exist in any Bourne-like shell that is compliant with POSIX 2008 (in POSIX 2004 it was an optional component only required on systems with the User Portability option, but then it became required everywhere as of the decade-old 2008 standard). The which program isn't guaranteed to exist anywhere, although Debian's policy document requires it.

Thanks for doing your part to help get us one step closer to a world in which the "which" program is not used. :)