OpenMW-CS: Generate record filters by drag & dropping cell content to the filters field

This is an already solved issue, a pair to !2617 (merged)

This really nice improvement allows users to drag and drop cell content to the filters field and generate appropriate record filters. As documented here https://openmw.readthedocs.io/en/latest/manuals/openmw-cs/records-drag-and-drop.html#filtering