Make context and dropdown menus scrollable (#15127)

This PR makes context and dropdown menus scrollable, so that they don't
become totally unusable when they overflow the window.

Release Notes:

- N/A

crates/ui/src/components/context_menu.rs

@@ -311,7 +311,10 @@ impl Render for ContextMenu {
         div().occlude().elevation_2(cx).flex().flex_row().child(
             WithRemSize::new(ui_font_size).flex().child(
                 v_flex()
+                    .id("context-menu")
                     .min_w(px(200.))
+                    .max_h(vh(0.75, cx))
+                    .overflow_y_scroll()
                     .track_focus(&self.focus_handle)
                     .on_mouse_down_out(cx.listener(|this, _, cx| this.cancel(&menu::Cancel, cx)))
                     .key_context("menu")