💥 Refactor add-hook! macro & change arg order

This update may potentially break your usage of add-hook! if you pass
the :local or :append properties to it. This is how they used to work:

  (add-hook! :append 'some-mode-hook #'do-something)

Thsoe properties must now follow the hooks, e.g.

  (add-hook! 'some-mode-hook :append #'do-something)

Other changes:
- Various add-hook calls have been renamed to add-hook! because I
  incorrectly assumed `defun` always returned its definition's symbol,
  when in fact, its return value is "undefined" (so sayeth the
  documentation). This should fix #1597.
- This update adds the ability to add multiple functions to hooks
  without a list:

    (add-hook! 'some-mode-hook
               #'do-something
               #'do-something-else)

- The indentation logic has been changed so that consecutive function
  symbols at indented at the same level as the first argument, but forms
  are indent like a defun.

    (add-hook! 'some-mode-hook
               #'do-something
               #'do-something-else)

    (add-hook! 'some-mode-hook
      (message "Hello"))

modules/ui/vc-gutter/config.el

@@ -22,7 +22,7 @@ to the right fringe.")
 (use-package! git-gutter
   :commands git-gutter:revert-hunk git-gutter:stage-hunk
   :init
-  (add-hook 'find-file-hook
+  (add-hook! 'find-file-hook
     (defun +vc-gutter-init-maybe-h ()
       "Enable `git-gutter-mode' in the current buffer.
 
@@ -67,7 +67,7 @@ is deferred until the file is saved. Respects `git-gutter:disabled-modes'."
   ;; Update git-gutter on focus (in case I was using git externally)
   (add-hook 'focus-in-hook #'git-gutter:update-all-windows)
 
-  (add-hook! :append '(doom-escape-hook doom-switch-window-hook)
+  (add-hook! '(doom-escape-hook doom-switch-window-hook) :append
     (defun +vc-gutter-update-h (&rest _)
       "Refresh git-gutter on ESC. Return nil to prevent shadowing other
 `doom-escape-hook' hooks."