vimPlugins: turn filetype and syntax before sourcing the plugins (#66536)

Vim Terraform expects the `filetypedetect` group to exist. However, since we were enabling the filetype and the syntax *after* loading the plugins, it was exiting with an error preventing us from generating the remote plugins manifest with the plugin enabled. See #65894 for context.

pkgs/applications/editors/neovim/wrapper.nix

···
         # Only display the log on error since it will contain a few normally
         # irrelevant messages.
         if ! $out/bin/nvim \
-          -u ${vimUtils.vimrcFile (configure // { customRC = ""; })} \
+          -u ${vimUtils.vimrcFile (configure // { customRC = ""; beforePlugins = ''filetype indent plugin on | syn on''; })} \
           -i NONE -n \
           -E -V1rplugins.log -s \
           +UpdateRemotePlugins +quit! > outfile 2>&1; then

pkgs/misc/vim-plugins/vim-utils.nix

···
     vam ? null,
     pathogen ? null,
     plug ? null,
-    customRC ? ""
+    customRC ? "",
+    beforePlugins ? "",
   }:
 
     let
···
   in writeText "vimrc" ''
   " minimal setup, generated by NIX
   set nocompatible
+
+  ${beforePlugins}
 
   ${vamImpl}
   ${pathogenImpl}