fix: add :depth field to modules

This introduces a depth field for modules so that they may dictate their
load order explicitly, it also treats depths <= -100 or >= 100 as
special depths, which will be loaded early, before their respective
doom-{before,after}-module-{init,config}-hook. This permits psuedo
modules like :core and :user modules to be treated as normal modules
without too many special cases.

This also fixes a module load order issue on Emacs 29 (#6813), caused by
emacs-mirror/emacs@4311bd0bd7, which changed the return value order of
hash-table-{keys,values} causing modules to be loaded in reverse order;
resulting in the loss of evil keybinds, among other things.

Other notable changes:
- Changes the data structure for module data caches from a list to a
  vector. Uses less memory and permits faster lookups. Also adds two
  depth fields to the front of it.
- Changes the signature of doom-module-list and doom-package-list.
- Renames doom--read-packages -> doom-packages--read for consistency
  with naming convention.
- Add doom-module-depth function.
- Adds a temporary doom-core-dir/init.el file, which is responsible for
  loading doom-*.el.

Fix: #6813
Ref: emacs-mirror/emacs@4311bd0bd7

lisp/doom.el

@@ -36,10 +36,10 @@
 ;;     > $EMACSDIR/lisp/doom.el
 ;;       - $EMACSDIR/lisp/doom-lib.el
 ;;     > $EMACSDIR/lisp/doom-start.el
-;;       - $EMACSDIR/doom-{keybinds,ui,projects,editor}.el
 ;;       - hook: `doom-before-init-hook'
 ;;       - $DOOMDIR/init.el
-;;   > $XDG_DATA_HOME/doom/$PROFILE/@/curr/init.el   (replaces $EMACSDIR/init.el)
+;;   > $XDG_DATA_HOME/doom/$PROFILE/@/$VERSION/init.el   (replaces $EMACSDIR/init.el)
+;;     - $EMACSDIR/doom-{keybinds,ui,projects,editor}.el
 ;;     - hook: `doom-before-modules-init-hook'
 ;;     - {$DOOMDIR,$EMACSDIR}/modules/*/*/init.el
 ;;     - hook: `doom-after-modules-init-hook'