Major refactor & optimization of how modules load their packages

Now that we are loading package autoloads files (as part of the
generated doom-package-autoload-file when running make autoloads), many
:commands properties are redundant. In fact, many def-package! blocks
are redundant.

In some cases, we can do without a config.el file entirely, and can move
into the autoloads file or rely entirely on package autoloads.

Also, many settings have been moved in their module's autoloads files,
which makes them available ASAP; their use no longer depends on module
load order.

This gained me a modest ~10% boost in startup speed.

modules/feature/lookup/autoload/docsets.el

@@ -0,0 +1,40 @@
+;;; feature/lookup/autoload/docsets.el -*- lexical-binding: t; -*-
+;;;###if (featurep! +docsets)
+
+;;;###autoload
+(def-setting! :docset (modes &rest docsets)
+  "Registers a list of DOCSETS (strings) for MODES (either one major mode
+symbol or a list of them).
+
+If MODES is a minor mode, you can use :add or :remove as the first element of
+DOCSETS, to instruct it to append (or remove) those from the docsets already set
+by a major-mode, if any.
+
+Used by `+lookup/in-docsets' and `+lookup/documentation'."
+  (let* ((modes (doom-unquote modes))
+         (ivy-p (featurep! :completion ivy))
+         (hook-sym (intern (format "+lookup|%s-docsets--%s"
+                                   (cond ((eq ',(car docsets) :add)    'add)
+                                         ((eq ',(car docsets) :remove) 'remove)
+                                         ('set))
+                                   (string-join docsets "-"))))
+         (var-sym (if ivy-p 'counsel-dash-docsets 'helm-dash-docsets)))
+    `(progn
+       (defun ,hook-sym ()
+         (make-variable-buffer-local ',var-sym)
+         ,(cond ((eq ',(car docsets) :add)
+                 `(setq ,var-sym (append ,var-sym (list ,@(cdr docsets)))))
+                ((eq ',(car docsets) :remove)
+                 `(setq ,var-sym
+                        (cl-loop with to-delete = (list ,@(cdr docsets))
+                                 for docset in ,var-sym
+                                 unless (member docset to-delete)
+                                 collect docset)))
+                (`(setq ,var-sym (list ,@docsets)))))
+       (add-hook! ,modes #',hook-sym))))
+
+;;;###autoload
+(autoload 'helm-dash-installed-docsets "helm-dash")
+
+;;;###autoload
+(autoload 'helm-dash-docset-installed-p "helm-dash")