Toggle & Switch (#21979)

![CleanShot 2024-12-13 at 11 27
39@2x](https://github.com/user-attachments/assets/7c7828c0-c5c7-4dc6-931e-722366d4f15a)

- Adds the Switch component
- Updates `Selected`, `Selectable` -> `ToggleState`, `Toggleable`
- Adds `checkbox` and `switch` functions to align better with other
elements in our layout system.

We decided not to merge Switch and Checkbox. However, in a followup I'll
introduce a Toggle or AnyToggle enum so we can update
`CheckboxWithLabel` -> `ToggleWithLabel` as this component will work
exactly the same with either a Checkbox or a Switch.

Release Notes:

- N/A

crates/ui/src/utils.rs

@@ -1,5 +1,8 @@
 //! UI-related utilities
 
+use gpui::WindowContext;
+use theme::ActiveTheme;
+
 mod color_contrast;
 mod format_distance;
 mod search_input;
@@ -9,3 +12,8 @@ pub use color_contrast::*;
 pub use format_distance::*;
 pub use search_input::*;
 pub use with_rem_size::*;
+
+/// Returns true if the current theme is light or vibrant light.
+pub fn is_light(cx: &WindowContext) -> bool {
+    cx.theme().appearance.is_light()
+}