Reorganize common configuration

common/home-manager/nixvim/none-ls.nix

@@ -0,0 +1,32 @@
+{ ... }: {
+  programs.nixvim.plugins.none-ls = {
+    enable = true;
+    settings.on_attach = ''
+      function(client, bufnr)
+        if client.supports_method("textDocument/formatting") then
+          vim.api.nvim_clear_autocmds({ group = augroup, buffer = bufnr })
+          vim.api.nvim_create_autocmd("BufWritePre", {
+            group = augroup,
+            buffer = bufnr,
+            callback = function()
+              vim.lsp.buf.format({ async = false })
+            end,
+          })
+        end
+      end
+    '';
+    sources = {
+      formatting = {
+        black.enable = true;
+        dart_format.enable = true;
+        nixfmt.enable = true;
+        prettier = {
+          enable = true;
+          disableTsServerFormatter = true;
+          settings = { extra_filetypes = [ "svelte" ]; };
+        };
+        xmllint.enable = true;
+      };
+    };
+  };
+}