Add TrafficLights component (#3011)

This PR adds a `TrafficLights` component for GPUI2.

<img width="861" alt="Screenshot 2023-09-21 at 11 32 10 PM"
src="https://github.com/zed-industries/zed/assets/1486634/0fe0e847-49b3-44dc-bd4c-64f12f0051c1">

Release Notes:

- N/A

crates/ui/src/components.rs

@@ -2,11 +2,13 @@ mod facepile;
 mod follow_group;
 mod list_item;
 mod tab;
+mod traffic_lights;
 
 pub use facepile::*;
 pub use follow_group::*;
 pub use list_item::*;
 pub use tab::*;
+pub use traffic_lights::*;
 
 use std::marker::PhantomData;
 use std::rc::Rc;