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/dropdown_menu.rs

@@ -1,4 +1,4 @@
-use gpui::{ClickEvent, CursorStyle, MouseButton, View};
+use gpui::{AnchorCorner, ClickEvent, CursorStyle, MouseButton, View};
 
 use crate::{prelude::*, ContextMenu, PopoverMenu};
 
@@ -45,6 +45,7 @@ impl RenderOnce for DropdownMenu {
             .full_width(self.full_width)
             .menu(move |_cx| Some(self.menu.clone()))
             .trigger(DropdownMenuTrigger::new(self.label).full_width(self.full_width))
+            .attach(AnchorCorner::BottomLeft)
     }
 }