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/lang/latex/config.el

@@ -33,7 +33,7 @@
         font-latex-fontify-sectioning 1.15)
   (setq-default TeX-master nil)
   ;; Display the output of the latex commands in a popup.
-  (set! :popup " output\\*$" '((size . 15)))
+  (set-popup-rule! " output\\*$" '((size . 15)))
 
   ;; TeX Font Styling
   ;; (def-package! tex-style :defer t)
@@ -200,7 +200,7 @@
   :when (featurep! :completion company)
   :commands (company-auctex-init)
   :init
-  ;; We can't use the (set! :company-backend ...) because Auctex reports its
+  ;; We can't use the (set-company-backend! ...) because Auctex reports its
   ;; major-mode as `latex-mode', but uses LaTeX-mode-hook for its mode, which is
   ;; not anticipated by :company-backend (and shouldn't have to!)
   (add-hook! LaTeX-mode