Restructure ui into just elements and components (#3023)

This PR restructures the `ui` crate into just `elements` and
`components`.

This was already done on the `gpui2-ui` branch, just getting it onto
`main`.

Release Notes:

- N/A

---------

Co-authored-by: Nate Butler <nate@zed.dev>

crates/ui/src/elements.rs

@@ -1,7 +1,6 @@
 mod avatar;
 mod details;
 mod icon;
-mod icon_button;
 mod indicator;
 mod input;
 mod label;
@@ -11,7 +10,6 @@ mod tool_divider;
 pub use avatar::*;
 pub use details::*;
 pub use icon::*;
-pub use icon_button::*;
 pub use indicator::*;
 pub use input::*;
 pub use label::*;