💥 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"))

core/core-modules.el

@@ -472,11 +472,11 @@ to have them return non-nil (or exploit that to overwrite Doom's config)."
     (error "'%s' isn't a valid hook for use-package-hook!" when))
   `(progn
      (setq use-package-inject-hooks t)
-     (add-hook!
-       ',(intern (format "use-package--%s--%s-hook"
-                         package
-                         (substring (symbol-name when) 1)))
-       ,@body)))
+     (add-hook ',(intern (format "use-package--%s--%s-hook"
+                                 package
+                                 (substring (symbol-name when) 1)))
+               (lambda () ,@body)
+               'append)))
 
 (defmacro require! (category module &rest flags)
   "Loads the CATEGORY MODULE module with FLAGS.