Extract UI elements from storybook into new ui crate (#3008)

This PR extracts the various UI elements from the `storybook` crate into
a new `ui` library crate.

Release Notes:

- N/A

crates/ui/src/lib.rs

@@ -0,0 +1,14 @@
+#![allow(dead_code, unused_variables)]
+
+mod components;
+mod element_ext;
+mod elements;
+mod modules;
+pub mod prelude;
+mod theme;
+
+pub use components::*;
+pub use element_ext::*;
+pub use elements::*;
+pub use modules::*;
+pub use theme::*;