refactor!: restructure Doom core

BREAKING CHANGE: This restructures Doom's core in an effort to slim it
down and partially mirror architectural changes coming in v3. This is
part 2 of 3 commits (part 1 being 1590434), done to facilitate a change
in part 3 that will introduce a new `doom!` syntax for pulling
third-party module libraries from remote sources (similar to `package!`
statements). I am backporting this from V3 so I can move our modules out
into separate repos sooner than later, so development on modules can
continue separately without interfering with v3's roll out.

Though this is labeled a breaking change, it shouldn't affect most users
except those few tinkering directly with Doom's internals.

Ref: 15904349cf

lisp/lib/config.el

@@ -104,7 +104,7 @@ Runs `doom-after-reload-hook' afterwards."
   (interactive)
   (mapc #'require (cdr doom-incremental-packages))
   (doom--if-compile doom-reload-command
-      (with-doom-context '(reload modules)
+      (with-doom-context '(reload module)
         (doom-run-hooks 'doom-before-reload-hook)
         (doom-load (file-name-concat doom-user-dir doom-module-init-file) t)
         (with-demoted-errors "PRIVATE CONFIG ERROR: %s"
@@ -127,7 +127,7 @@ remove orphaned ones. It also doesn't reload your private config.
 It is useful to only pull in changes performed by 'doom sync' on the command
 line."
   (interactive)
-  (require 'doom-profiles)
+  (doom-require 'doom-lib 'profiles)
   ;; TODO: Make this more robust
   (with-doom-context 'reload
     (dolist (file (mapcar #'car doom-profile-generators))