* Use dropzone to handle file uploading for all cases, including pasting
and dragging
* Merge duplicate code, use consistent behavior for link generating
Close#20130
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Co-authored-by: silverwind <[email protected]>
Co-authored-by: wxiaoguang <[email protected]>
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
