feat(lang): Enable use of markdown-edit-code-block

This allows editing code blocks within markdown files in a separate
buffer with the proper language major-mode applied.

Also integrate it with recursive-narrow, so it can be triggered with via
narrowing commands.

modules/languages/siren-markdown.el

@@ -50,5 +50,9 @@
     (smartparens-mode +1)
     (subword-mode)))
 
+;; Required by markdown-edit-code-block.
+(use-package edit-indirect
+  :defer t)
+
 (provide 'siren-markdown)
 ;;; siren-markdown.el ends here

modules/navigation/siren-recursive-narrow.el

@@ -15,10 +15,15 @@
   :config
   (add-hook 'recursive-narrow-dwim-functions
             'siren-recursive-narrow-org-edit-src-code)
+  (add-hook 'recursive-narrow-dwim-functions
+            'siren-recursive-narrow-markdown-edit-code-block)
 
   :init
   (defun siren-recursive-narrow-org-edit-src-code()
-    (ignore-errors (org-edit-src-code) t)))
+    (ignore-errors (org-edit-src-code) t))
+
+  (defun siren-recursive-narrow-markdown-edit-code-block()
+    (ignore-errors (markdown-edit-code-block) t)))
 
 (provide 'siren-recursive-narrow)
 ;;; siren-recursive-narrow.el ends here