nvim-cmp: move text and snippet completions to the bottom

This doesn't guarantee that snippets will be above text completions, but
that should still be the case, since the `kind` comparator sorts
snippets above text.

modules/plugins/completion/nvim-cmp/config.nix

@@ -42,6 +42,20 @@ in {
             after = ''
               ${optionalString luasnipEnable "local luasnip = require('luasnip')"}
               local cmp = require("cmp")
+
+              local kinds = require("cmp.types").lsp.CompletionItemKind
+              local deprio = function(kind)
+                return function(e1, e2)
+                  if e1:get_kind() == kind then
+                    return false
+                  end
+                  if e2:get_kind() == kind then
+                    return true
+                  end
+                  return nil
+                end
+              end
+
               cmp.setup(${toLuaObject cfg.setupOpts})
 
               ${optionalString config.vim.lazy.enable

modules/plugins/completion/nvim-cmp/nvim-cmp.nix

@@ -29,6 +29,8 @@ in {
       sorting.comparators = mkOption {
         type = mergelessListOf (either str luaInline);
         default = [
+          (mkLuaInline "deprio(kinds.Text)")
+          (mkLuaInline "deprio(kinds.Snippet)")
           "offset"
           "exact"
           "score"
@@ -43,6 +45,12 @@ in {
           (see `:help cmp-config.sorting.comparators`),
           or a string, in which case the builtin comparator with that name will
           be used.
+
+          A `deprio` function and a `kinds`
+          (`require("cmp.types").lsp.CompletionItemKind`) variable is provided
+          above `setupOpts`. By passing a type to the funcion, the returned
+          function will be a comparator that always ranks the specified kind the
+          lowest.
         '';
         apply = map (
           c: