Problems when binding with codemirror6

[Benbinbin]

@percy507

But there are some limits. eg: The multiple selection can’t recover by undo action, because we use the history stack of prosemirror.

I also meet some problem when bind the codemirror with prosemirror, and figure out another solution about the selection recover, the key point is record the codemirror selection in the code_block node attribute, and then reload it when we need, this solution can support multiple selection inside the codemirror