ui: add show_pointer

For showing the cursor when hovering over a clickable thing. We need
this in more places.

Signed-off-by: William Casarin <jb55@jb55.com>

crates/notedeck_columns/src/ui/mod.rs

@@ -59,3 +59,7 @@ pub fn hline(ui: &egui::Ui) {
     let stroke = ui.style().visuals.widgets.noninteractive.bg_stroke;
     ui.painter().hline(rect.x_range(), resize_y, stroke);
 }
+
+pub fn show_pointer(ui: &egui::Ui) {
+    ui.ctx().set_cursor_icon(egui::CursorIcon::PointingHand);
+}