gpui: Fix `show: false` support on Windows to create an invisible window (#18161)

Release Notes:

- N/A
- 
The `show` of WindowOptions is valid on macOS but not on Windows, this
changes to fix it to support create an invisible window.

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

## Before



https://github.com/user-attachments/assets/4157bdaa-39a7-44df-bbdc-30b00e9c61e9


## After



https://github.com/user-attachments/assets/d48fa524-0caa-4f87-932d-01d7a468c488


https://github.com/user-attachments/assets/dd052f15-c8db-4a2a-a6af-a7c0ffecca84