lang/org: refactor contrib modules

- Fix #1546
- Ensure contrib modules aren't included in byte-compilation/autoload
  generation if their requisite flags aren't enabled

modules/lang/org/autoload/contrib-dragndrop.el

@@ -0,0 +1,39 @@
+;;; lang/org/autoload/contrib-dragndrop.el -*- lexical-binding: t; -*-
+;;;###if (featurep! +dragndrop)
+
+;;;###autoload
+(defun +org-dragndrop-download-dnd (uri action)
+  "TODO"
+  (if (eq major-mode 'org-mode)
+      (+org-attach/uri uri)
+    (let ((dnd-protocol-alist
+           (rassq-delete-all '+org-attach-download-dnd
+                             (copy-alist dnd-protocol-alist))))
+      (dnd-handle-one-url nil action uri))))
+
+;;;###autoload
+(defun +org-dragndrop*insert-link (_link filename)
+    "Produces and inserts a link to FILENAME into the document.
+
+If FILENAME is an image, produce an attach:%s path, otherwise use file:%s (with
+an file icon produced by `+org-attach--icon')."
+    (if (looking-back "^[ \t]+" (line-beginning-position))
+        (delete-region (match-beginning 0) (match-end 0))
+      (newline))
+    (cond ((image-type-from-file-name filename)
+           (insert
+            (concat (if (= org-download-image-html-width 0) ""
+                      (format "#+attr_html: :width %dpx\n" org-download-image-html-width))
+                    (if (= org-download-image-latex-width 0) ""
+                      (format "#+attr_latex: :width %dcm\n" org-download-image-latex-width))
+                    (cond ((file-in-directory-p filename org-attach-directory)
+                           (format "[[attach:%s]]" (file-relative-name filename org-attach-directory)))
+                          ((file-in-directory-p filename org-directory)
+                           (format org-download-link-format (file-relative-name filename org-directory)))
+                          ((format org-download-link-format filename)))))
+           (org-display-inline-images))
+          ((insert
+            (format "%s [[./%s][%s]] "
+                    (+org-attach--icon filename)
+                    (file-relative-name filename (file-name-directory buffer-file-name))
+                    (file-name-nondirectory (directory-file-name filename)))))))