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/ui/popup/+hacks.el

@@ -209,7 +209,7 @@ the command buffer."
 
 ;;;###package helm
 ;;;###package helm-ag
-(when (featurep! :completion helm)
+(when (modulep! :completion helm)
   (setq helm-default-display-buffer-functions '(+popup-display-buffer-stacked-side-window-fn))
 
   ;; Fix #897: "cannot open side window" error when TAB-completing file links

modules/ui/popup/config.el

@@ -41,7 +41,7 @@ adjustment.")
 
 (defvar +popup-buffer-mode-map
   (let ((map (make-sparse-keymap)))
-    (when (featurep! :editor evil)
+    (when (modulep! :editor evil)
       ;; For maximum escape coverage in emacs state buffers; this only works in
       ;; GUI Emacs, in tty Emacs use C-g instead
       (define-key map [escape] #'doom/escape))
@@ -127,10 +127,10 @@ prevent the popup(s) from messing up the UI (or vice versa)."
 ;; Default popup rules & bootstrap
 
 (set-popup-rules!
-  (when (featurep! +all)
+  (when (modulep! +all)
     '(("^\\*"  :slot 1 :vslot -1 :select t)
       ("^ \\*" :slot 1 :vslot -1 :size +popup-shrink-to-fit)))
-  (when (featurep! +defaults)
+  (when (modulep! +defaults)
     '(("^\\*Completions" :ignore t)
       ("^\\*Local variables\\*$"
        :vslot -1 :slot 1 :size +popup-shrink-to-fit)