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/assistant2/src/message_editor.rs

@@ -268,8 +268,8 @@ impl Render for MessageEditor {
                         self.use_tools.into(),
                         cx.listener(|this, selection, _cx| {
                             this.use_tools = match selection {
-                                Selection::Selected => true,
-                                Selection::Unselected | Selection::Indeterminate => false,
+                                ToggleState::Selected => true,
+                                ToggleState::Unselected | ToggleState::Indeterminate => false,
                             };
                         }),
                     )))