add cell.setEdited and table.setCellEdited features

[nmih]

Implements feature request https://github.com/olifolkerd/tabulator/issues/4443

This adds a new function to the cell component setEdited and the table component setCellEdited that allows a developer to programmatically mark a cell as edited. The rationale is in the linked issue - basically we want to be able to control this flag and also provide a mirror function to clearEdited.

This has been tested by manually calling the method, checking the isEdited() method to see if it is true, and finally by calling table.getEditedCells() to see if the cell shows up in that array.