Continue #39876 to add `disabled` state to `MenuItem`.
Make this change for #44047 ready to have disabled state.
1. Add `disabled` state to `MenuItem`.
2. Add some builder methods to `Menu` and `MenuItem`.
3. Improve `set_menus` method to receive a `impl IntoIterator<Item =
Menu>`.
Release Notes:
- N/A
--
<img width="294" height="204" alt="image"
src="https://github.com/user-attachments/assets/688e0db8-6c4e-4f9b-a832-8228db0e95d8"
/>
```bash
cargo run -p gpui --example set_menus
```
Jason Lee
d8fea89fce