Closes #52774

## Summary
- Bind Windows `Alt+F4` to `workspace::CloseWindow` in the `Terminal`
keymap context
- Add a regression test covering the built-in Windows terminal keymap
entry

## Why
When the integrated terminal is focused, `Alt+F4` should close the
window instead of falling through to terminal keystroke handling.
Handling this in the Windows `Terminal` keymap keeps the fix aligned
with the rest of the terminal shortcut overrides.

## Validation
- `cargo test -p settings
windows_terminal_keymap_closes_window_on_alt_f4`

Release Notes:

- Fixed Alt+F4 on Windows so Zed closes even when the integrated
terminal is focused.

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Co-authored-by: Jakub Konka <kubkon@jakubkonka.com>