There is a drawback in 12048bd6, if a kanban view with an
"Undefined" column (exist when a kanban view grouped on a relational
field and some record have this field unset) had a column resequenced a
traceback would happen if more than one column was displayed.
This happen because before we had a "undefined" ID for the "Undefined"
column and after 12048bd6 we get a framework unique ID which was not
managed.
note: this commit also adds `left`/`right` values in the dragAndDrop
test utility function so an element can be dropped at the right/left of
another element.
related to opw-782433
closes#21708
Nicolas Lempereur
46cf7f17a3