refactor: minor refactors & commentary revision

* lisp/doom-cli.el:
  - reference backport source commit.
  - doom-cli--restart: a type check is all we need here. This is a
    programmer error, not a user error.
* lisp/doom-editor.el (recentf): mention recentf-show-abbreviated (added in
  emacs-mirror/emacs@32906819ad)
* lisp/doom-keybinds.el (doom-init-leader-keys-h): move to
  doom-after-init-hook, in case the user customizes leader variables in
  a previous hook (like emacs-startup-hook or after-init-hook).
* lisp/doom-start.el: use eval-when! to compile out the section on
  non-macOS systems (when Doom gets around to compiling its core files,
  later).
* modules/config/literate/autoload.el (+literate-config-file): use
  file-name-concat instead of string concat. This relaxes the
  requirement that doom-user-dir end in a /; a requirement I intend to
  fully phase out.
* modules/lang/emacs-lisp/autoload.el (+emacs-lisp-non-package): remove
  empty map! macro in flycheck-emacs-lisp-check-form. The macro already
  no-ops at compile-time/in noninteractive sessions since b480ed51a3.
* modules/ui/hl-todo/config.el (hl-todo-keyword-faces): revise
  commentary for default hl-todo keywords.

Ref: emacs-mirror/emacs@32906819ad
Ref: b480ed51a3

modules/config/literate/autoload.el

@@ -2,8 +2,7 @@
 
 ;;;###autoload (add-hook 'org-mode-hook #'+literate-enable-recompile-h)
 
-(defvar +literate-config-file
-  (concat doom-user-dir "config.org")
+(defvar +literate-config-file (file-name-concat doom-user-dir "config.org")
   "The file path of your literate config file.")
 
 (defvar +literate-tangle--async-proc nil)
@@ -144,3 +143,5 @@ config, and should trigger a recompile if changed."
         (buffer-file-name (buffer-base-buffer))
         (file-name-directory +literate-config-file))
        (+literate-tangle-h)))
+
+;;; autoload.el ends here