Refactor Doom core init process (again)

- Eager-load all core autoloaded libraries if autoloads file isn't
  present.
- Renames functions to be more descriptive of their true purpose:
  - doom-initialize-autoloads -> doom-load-autoloads-file
  - doom-load-env-vars -> doom-load-envvars-file
- Use doom-module-p instead of featurep! for backend use (the latter is
  mainly syntax sugar for module use, and evaluates at compile/expansion
  time, which may cause hash-table-p errors early in the startup
  process).
- Reorder plist library to prevent load order race condition with the
  functions using the macros that haven't been defined yet.

core/cli/byte-compile.el

@@ -91,8 +91,8 @@ If RECOMPILE-P is non-nil, only recompile out-of-date files."
 
       ;; But first we must be sure that Doom and your private config have been
       ;; fully loaded. Which usually aren't so in an noninteractive session.
-      (doom-initialize-autoloads doom-autoload-file)
-      (doom-initialize-autoloads doom-package-autoload-file)
+      (doom-load-autoloads-file doom-autoload-file)
+      (doom-load-autoloads-file doom-package-autoload-file)
 
       ;;
       (unless target-dirs