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

bin/doom

@@ -302,14 +302,12 @@ SEE ALSO:
     ;; (load! "test" dir)
     )
 
-  (let ((cli-file "cli"))
+  (let ((cli-file "cli.el"))
     (defcli-group! "Module commands"
       (dolist (key (doom-module-list))
-        (when-let (path (doom-module-expand-path (car key) (cdr key) cli-file))
-          (defcli-group! :prefix (format "+%s" (cdr key))
-            (doom-load path t)))))
-
-    (load! cli-file doom-user-dir t))
+        (when-let (path (doom-module-locate-path (car key) (cdr key) cli-file))
+          (defcli-group! :prefix (if (cdr key) (format "+%s" (cdr key)))
+            (doom-load (file-name-sans-extension path)))))))
 
   ;; Allow per-project Doom settings in .doom files.
   (let (doomrc)