Consider DecoratorNode in $insertNodeToNearestRoot

[LvChengbin]

DecoratorNode is not treated as ElementNode from this commit (#5371) on, but In $insertNodeToNearestRoot method, getTopLevelElementOrThrow is called if the selection is not a range selection. It causes error while the focus node is a DecoratorNode.

lexical/packages/lexical-utils/src/index.ts

Line 473 in 686217d

nodes[nodes.length - 1].getTopLevelElementOrThrow().insertAfter(node);

And another feature in this method should which I think it should be modified is checking empty after splitting node in range selection, otherwise it may create one more empty line.

Another question is why does this method end with inserting another paragraph node?