TagMultiselectWidget: populate input with item label on backspace
TagMultiselectWidget: populate input with item label on backspace

If a user presses backspace when the input is empty, the tag
should disappear, and the input should be populated with the
tag's label rather than its data, since the user may never have
seen the data before, but will definitely have seen the label, in
the tag itself.

Bug: T216075
Change-Id: Ie11bb2de2bc023c631eb4ddcfb343784dacd6ce0

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui