refactor!: move helpful from :core to :lang emacs-lisp

BREAKING CHANGE: This moves helpful.el out of core into :lang
emacs-lisp. Since most (all) people have this module enabled, this
shouldn't make a difference for most people, but if you're one of the
few that don't have :lang emacs-lisp enabled, Doom will revert to using
Emacs' built-in help.el and describe-* commands.

Others can also disable helpful with (package! helpful :disable t) if
they prefer Emacs' built-in help system, which wasn't possible before,
because it was a core package.

This was done as part of an ongoing effort to slim down Doom's core in
preparation for v3.

modules/editor/evil/config.el

@@ -150,15 +150,6 @@ directives. By default, this only recognizes C directives.")
     :after-until #'evil-global-marker-p
     (and (>= char ?2) (<= char ?9)))
 
-  ;; HACK Invoking helpful from evil-ex throws a "No recursive edit is in
-  ;;      progress" error because, between evil-ex and helpful,
-  ;;      `abort-recursive-edit' gets called one time too many.
-  (defadvice! +evil--fix-helpful-key-in-evil-ex-a (key-sequence)
-    :before #'helpful-key
-    (when (evil-ex-p)
-      (run-at-time 0.1 nil #'helpful-key key-sequence)
-      (abort-recursive-edit)))
-
   ;; Make J (evil-join) remove comment delimiters when joining lines.
   (advice-add #'evil-join :around #'+evil-join-a)
 
@@ -464,9 +455,6 @@ directives. By default, this only recognizes C directives.")
        :v  "gR"  #'+eval:replace-region
        ;; Restore these keybinds, since the blacklisted/overwritten gr/gR will
        ;; undo them:
-       (:after helpful
-        :map helpful-mode-map
-        :n "gr" #'helpful-update)
        (:after compile
         :map (compilation-mode-map compilation-minor-mode-map)
         :n "gr" #'recompile)