gpui: Fix TextStyle default font_family crash on Windows, use Segoe UI for Windows (#14040)

Release Notes:

- Fixed default font_family crash on Windows, use `Segoe UI`.

## Crash error message

```
thread 'main' panicked at crates\gpui\src\text_system.rs:150:9:
failed to resolve font 'Helvetica' or any of the fallbacks: 
Zed Plex Mono, Helvetica, Cantarell, Ubuntu, Noto Sans, DejaVu Sans
```

crates/gpui/src/text_system.rs

@@ -66,6 +66,7 @@ impl TextSystem {
                 // We should allow GPUI users to provide their own fallback font stack.
                 font("Zed Plex Mono"),
                 font("Helvetica"),
+                font("Segoe UI"),  // Windows
                 font("Cantarell"), // Gnome
                 font("Ubuntu"),    // Gnome (Ubuntu)
                 font("Noto Sans"), // KDE