pkg: vim highlights dune lockfiles as if they were virata config files

[gridbugs]

Vim treats the .pkg file extension as "Virata AConfig Configuration Script Syntax" (https://www.vim.org/scripts/script.php?script_id=930). This leads to confusing highlighting E.g. the % character is treated as the start of a comment, and $VARIABLES are highlighted as if only the first character is the variable, similar to in Makefiles.

I propose that we change the extension to .dune_pkg to avoid this confusion.

[rgrinberg]

How about we just updated vim-ocaml to override this for dune.lock/foo.pkg? files. It doesn't seem like a good trade-off to add cruft to our stuff to satisfy the tiny fraction of users that use "Virata".

[gridbugs]

It's not about virata users. Vim comes with virata syntax highlighting out of the box so all vim users see the virata syntax highlighting when editing .pkg files.

[emillon]

I agree with Rudi, it's fairly easy to change vim-ocaml to support this.

[gridbugs]

It looks like vim comes with syntax highlighting for ocaml and dune files out of the box (checked by installing vim and neovim in an empty docker image). I just realized that I never installed syntax highlighting vim packages for ocaml on my machine. I wonder how many other ocaml developers never installed ocaml-vim.