Add a new action for inserting a new line above the current line. @ForLoveOfCats  also helped fix a bug among other things. When two collaborators had their cursors at the end of a line, and one collaborator performed a newline below action, the second collaborator's cursor would be dragged to the new line. This is also fixing that.

Co-Authored-By: Julia <30666851+ForLoveOfCats@users.noreply.github.com>