Improve markdown editor: width, height, preferred (#23895)
Follow #23876
1. Fine tune the heights of the editors (like before)
* Auto expand the editor (increase/decrease the height) when editing
2. Remember user's last used editor (textarea/easymde) in LocalStorage,
then next time the editor will be switched automatically
* No need to introduce extra config option, it satisfies all users,
including who prefer EasyMDE
3. Also fix the width problem of Review Panel
Screenshot:
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Co-authored-by: silverwind <me@silverwind.io>
