New :editor format module

Centralized code formatting with built-in support for a variety of
languages. Provides the set-formatter! function for defining your own.

Still experimental and needs more testing!

modules/lang/sh/config.el

@@ -67,6 +67,4 @@
 (def-package! fish-mode
   :when (featurep! +fish)
   :defer t
-  :config
-  (add-hook! fish-mode
-    (add-hook 'before-save-hook #'fish_indent-before-save)))
+  :config (set-formatter! 'fish-mode #'fish_indent))