Selecting filter on a column should add an extra filter row rather than clearing old filters if present

It would be great if currently setup filters would not be overwritten if selecting filter on an extra column. Instead, the extra row should appear with that column selected.

Start from the column filter selection UI described in the issue and trace how selecting another column currently replaces the existing filters. The work is done when selecting an additional column preserves the current filters and displays a new row for that column; verify the behavior with multiple filters already configured.

Written by the indexing model from the issue text.