Motivation for this change

• It requires gopls, but it's missing because it's no longer provided by gotools.
• It was relying on PATH to find the Go compiler. I've made an update to the plugin so it relies on g:go_bin_path when calling system() or when starting a job. I've filed a pull request upstream to fix this: Respect g:go_bin_path when start a job or when calling system() fatih/vim-go#2876

Note My patch upstream works for Linux but will definitely break Windows support. I'm not sure we have any Windows use case for this.

nix-shell -I nixpkgs=. \
	--pure \
	-p which \
	-p 'with import <nixpkgs> {}; neovim.override { configure = { vam.pluginDictionaries = [ "vim-go" ]; }; }' \
		--run 'cd /path/to/project; export GOPATH=/path/to/gopath; vim main.go'

nix-shell -I nixpkgs=. \
	--pure \
	-p which \
	-p 'with import <nixpkgs> {}; vim_configurable.customize { name = "vim"; vimrcConfig.packages.myVimPackage = with pkgs.vimPlugins; { start = [ vim-go ]; }; }' \
		--run 'cd /path/to/project; export GOPATH=/path/to/gopath; vim main.go'

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.