LibGUI: Respect Model::Role::BackgroundColor

This implementation is very gappy, but the basic feature allows us to
highlight cells with a custom background color.

Libraries/LibGUI/TableView.cpp

@@ -131,6 +131,11 @@ void TableView::paint_event(PaintEvent& event)
                         text_color = is_focused() ? palette().selection_text() : palette().inactive_selection_text();
                     else
                         text_color = model()->data(cell_index, Model::Role::ForegroundColor).to_color(palette().color(foreground_role()));
+                    auto cell_background_color = model()->data(cell_index, Model::Role::BackgroundColor);
+                    if (cell_background_color.is_valid()) {
+                        // FIXME: If all cells on a row provide a color, we should really fill the whole row!
+                        painter.fill_rect(cell_rect, cell_background_color.to_color(background_color));
+                    }
                     painter.draw_text(cell_rect, data.to_string(), font, column_metadata.text_alignment, text_color, Gfx::TextElision::Right);
                 }
             }