gpui: Remove use of use gpui::* in examples (#22311)

This PR removes the use of `use gpui::*` in the GPUI examples, as this
is not how consumers should be importing GPUI.

Release Notes:

- N/A

crates/gpui/examples/uniform_list.rs

@@ -1,4 +1,7 @@
-use gpui::*;
+use gpui::{
+    div, prelude::*, px, rgb, size, uniform_list, App, AppContext, Bounds, ViewContext,
+    WindowBounds, WindowOptions,
+};
 
 struct UniformListExample {}