feat(language/xml): add xmllint formatter setup and bind to C-c C-f

modules/languages/siren-xml.el

@@ -13,6 +13,10 @@
   :defer t
   :hook (nxml-mode . siren-xml-setup)
 
+  :general
+  (:keymaps 'nxml-mode-map
+            "C-c C-f" 'xmllint-format-buffer)
+
   :custom
   (nxml-attribute-indent 2)
   (nxml-child-indent 2)
@@ -20,7 +24,13 @@
   :preface
   (defun siren-xml-setup ()
     (run-hooks 'prog-mode-hook)
-    (setq-local tab-width 2)))
+    (setq-local tab-width 2))
+
+  :config
+  (reformatter-define xmllint-format
+    :program "xmllint"
+    :args '("--format" "-")
+    :lighter " XMLlint"))
 
 (provide 'siren-xml)
 ;;; siren-xml.el ends here