Redesign Doom bootstrap, caching & autoload generation logic

The autoloads file has been split into doom-autoload-file and
doom-package-autoload-file. The former is for Doom's modules and
standard library; the latter is for compiling all package autoloads like
load-path and auto-mode-alist (among other things).

This reduced my startup speed from ~1s to ~0.5s

init.el

@@ -31,5 +31,3 @@
       load-prefer-newer noninteractive)
 
 (require 'core (concat user-emacs-directory "core/core"))
-(when noninteractive
-  (require 'core-dispatcher))