Multiple column support in UI list

[Jiri Svoboda]

UI list control should allow multiple columns (and headers). A prime example where this would be used is in file list (Navigator, file dialogs) to provide file details (size, date).

Given the relatively static nature of columns we might simply provide data for multiple columns as a single string with e.g. tab separator ("myfile.txt\t10 kB\t2026-04-01 12:34:56"), similar to how we do it in the table formatter.