We change the current logic: instead of writing an init.vim which loads
lua/init-home-manager.lua, we write an init.lua that sources init.vim
This commit also avoids writing any of these files if the plugins have
no config.
This adds two new options: 'programs.neovim.coc.{enable,settings}`.
These settings offer a simple interface over `xdg.configFile."nvim/coc-settings.json`,
using the standard Nix' syntax instead of a multiline string.
* neovim: write config in $XDG_CONFIG_HOME/init.vim
instead of wrapping the configuration, which has sideeffects
https://github.com/NixOS/nixpkgs/issues/55376
* fix: update test accordingly
* neovim: allow setting init.vim config alongside plugins
* neovim: add test for neovim plugins
* neovim: make pluginWithConfigType a have type submodule
