Include package autoloads in doom-autoloads-file

This offloads some of the work Doom has to do creating
`doom-packages-file` onto `make autoloads`. This closely mimics the
package-quickstart-refresh functionality in Emacs 27+, but is more
specialized.

This means package autoloads are now loaded on every startup.

Many :mode, :interpreter, and :commands declarations in def-package!
blocks are made redundant by this and will be cleaned up soon.

core/core.el

@@ -107,10 +107,6 @@ XDG directory conventions if ~/.config/doom exists.")
 (defvar doom-init-hook nil
   "A list of hooks run when DOOM is initialized.")
 
-(defvar doom-internal-init-hook nil
-  "Hooks run after Doom has loaded all init.el files, and is ready to load
-modules.")
-
 
 ;;
 ;; Emacs fixes/hacks