refactor: deprecate featurep! for modulep!

featurep! will be renamed modulep! in the future, so it's been
deprecated. They have identical interfaces, and can be replaced without
issue.

featurep! was never quite the right name for this macro. It implied that
it had some connection to featurep, which it doesn't (only that it was
similar in purpose; still, Doom modules are not features). To undo such
implications and be consistent with its namespace (and since we're
heading into a storm of breaking changes with the v3 release anyway),
now was the best opportunity to begin the transition.

modules/app/irc/config.el

@@ -141,7 +141,7 @@ playback.")
   ;; Fail gracefully if not in a circe buffer
   (global-set-key [remap tracking-next-buffer] #'+irc/tracking-next-buffer)
 
-  (when (featurep! :completion vertico)
+  (when (modulep! :completion vertico)
     (after! consult
       (add-to-list 'consult-buffer-sources '+irc--consult-circe-source 'append)))
 
@@ -198,7 +198,7 @@ playback.")
   (define-key lui-mode-map "\C-u" #'lui-kill-to-beginning-of-line)
   (setq lui-fill-type nil)
 
-  (when (featurep! :checkers spell)
+  (when (modulep! :checkers spell)
     (setq lui-flyspell-p t))
 
   (after! evil