Move the LoadingLabel component to the UI crate (#33893)

So we can use it in other places and don't require them to depend on the
`agent_ui`. This PR also renames it from `AnimatedLabel` to
`LoadingLabel`.

Release Notes:

- N/A

crates/agent_ui/src/ui.rs

@@ -1,5 +1,4 @@
 mod agent_notification;
-mod animated_label;
 mod burn_mode_tooltip;
 mod context_pill;
 mod onboarding_modal;
@@ -7,7 +6,6 @@ pub mod preview;
 mod upsell;
 
 pub use agent_notification::*;
-pub use animated_label::*;
 pub use burn_mode_tooltip::*;
 pub use context_pill::*;
 pub use onboarding_modal::*;