Introduce autodefs to replace some settings

+ :popup -> set-popup-rule!
+ :popups -> set-popup-rules!
+ :company-backend -> set-company-backend!
+ :evil-state -> set-evil-initial-state!

I am slowly phasing out the setting system (def-setting! and set!),
starting with these.

What are autodefs? These are functions that are always defined, whether
or not their respective modules are enabled. However, when their modules
are disabled, they are replaced with macros that no-op and don't
waste time evaluating their arguments.

The old set! function will still work, for a while.

modules/completion/ivy/config.el

@@ -86,7 +86,7 @@ immediately runs it on the current candidate (ending the ivy session)."
     [remap swiper]                   #'counsel-grep-or-swiper)
 
   :config
-  (set! :popup "^\\*ivy-occur" '((size . 0.35)) '((transient . 0) (quit)))
+  (set-popup-rule! "^\\*ivy-occur" '((size . 0.35)) '((transient . 0) (quit)))
 
   (setq counsel-find-file-ignore-regexp "\\(?:^[#.]\\)\\|\\(?:[#~]$\\)\\|\\(?:^Icon?\\)"
         ;; Add smart-casing and compressed archive searching (-zS) to default