Selectmenu: Filterable demo now filters/refreshes selectmenu widget

Fixes gh-7677

... and actually fixes a bug in the existing selectmenu-custom-filter demo whereby the filter input does not return to the popup if the menu is ever shown as a dialog.
This is a pretty ugly if why dont we just do `$(  ".filterable-select" ).attr( "id" ) + "-dialog" !== id`?