Release Notes:

- N/A

With a `tab_index` and `tab_stop` option to `FocusHandle` to us can
switch focus by `Tab`, `Shift-Tab`.

The `tab_index` is from
[WinUI](https://learn.microsoft.com/en-us/uwp/api/windows.ui.xaml.controls.control.tabindex?view=winrt-26100)
and [HTML
tabindex](https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Global_attributes/tabindex),
only the `tab_stop` is enabled that can be added into the `tab_handles`
list.

- Added `window.focus_next()` and `window.focus_previous()` method to
switch focus.
- Added `tab_index` to `InteractiveElement`.

```bash
cargo run -p gpui --example tab_stop
```


https://github.com/user-attachments/assets/ac4e3e49-8359-436c-9a6e-badba2225211