Fix :after-call deferred packages not loading

If you open emacs with a file (emacs file.txt), the file is switched to
before the switch-buffer hooks are set up. However, many core packages
are hooked to those switch-buffer hooks (to load when they're first
triggered). They miss the boat and don't get loaded.

These packages are now hooked onto after-find-file as well (and
immediately), which will fire when a file is opened, before or after
initialization.

Fixes #680

core/core-ui.el

@@ -308,7 +308,7 @@ DEFAULT is non-nil, set the default mode-line for all buffers."
 
 ;; highlight matching delimiters
 (def-package! paren
-  :after-call doom-before-switch-buffer-hook
+  :after-call post-command-hook
   :config
   (setq show-paren-delay 0.1
         show-paren-highlight-openparen t