component: Add component and component_preview crates to power UI components (#24456)

This PR formalizes design components with the Component and
ComponentPreview traits.

You can open the preview UI with `workspace: open component preview`.

Component previews no longer need to return `Self` allowing for more
complex previews, and previews of components like `ui::Tooltip` that
supplement other components rather than are rendered by default.

`cargo-machete` incorrectly identifies `linkme` as an unused dep on
crates that have components deriving `IntoComponent`, so you may need to
add this to that crate's `Cargo.toml`:

```toml
# cargo-machete doesn't understand that linkme is used in the component macro
[package.metadata.cargo-machete]
ignored = ["linkme"]
```

Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <git@maxdeviant.com>

crates/ui/src/prelude.rs

@@ -6,9 +6,11 @@ pub use gpui::{
     InteractiveElement, ParentElement, Pixels, Rems, RenderOnce, SharedString, Styled, Window,
 };
 
+pub use component::{example_group, example_group_with_title, single_example, ComponentPreview};
+pub use ui_macros::IntoComponent;
+
 pub use crate::styles::{rems_from_px, vh, vw, PlatformStyle, StyledTypography, TextSize};
 pub use crate::traits::clickable::*;
-pub use crate::traits::component_preview::*;
 pub use crate::traits::disableable::*;
 pub use crate::traits::fixed::*;
 pub use crate::traits::styled_ext::*;