* Use dropzone to handle file uploading for all cases, including pasting
and dragging
* Merge duplicate code, use consistent behavior for link generating
Close#20130
---------
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Almost works like GitHub
* use Tab/Shift-Tab to indent/unindent the selected lines
* use Enter to insert a new line with the same indentation and prefix