### Godot version

v4.0.beta17.mono.official [c40020513]

### System information

Windows 11 22H2

### Issue description

If a focused subwindow is destroyed, DisplayServerWindows may still attempt to send mouse motion events to that window, because `last_focused_window` isn't updated until another window is focused.

```
ERROR: Condition "!windows.has(p_window)" is true. Returning: Point2i()
   at: window_get_position (platform/windows/display_server_windows.cpp:999)
```

### Steps to reproduce

Run the MRP, click some non-Godot application window to focus it, then click the "CLOSE" button in the secondary window. This destroys the window without re-focusing the main window, so hovering the mouse over the main window will produce the error message above.

### Minimal reproduction project

[native_windows_hover.zip](https://github.com/godotengine/godot/files/10573386/native_windows_hover.zip)

EnumRefreshRateData *data = (EnumRefreshRateData *)dwData;
	if (data->count == data->screen) {
		MONITORINFOEXW minfo;
		memset(&minfo, 0, sizeof(minfo));
		minfo.cbSize = sizeof(minfo);
		GetMonitorInfoW(hMonitor, &minfo);
		DEVMODEW dm;
		memset(&dm, 0, sizeof(dm));
		dm.dmSize = sizeof(dm);
		EnumDisplaySettingsW(minfo.szDevice, ENUM_CURRENT_SETTINGS, &dm);
		data->rate = dm.dmDisplayFrequency;
	}
	data->count++;
	return TRUE;
}
Rect2i DisplayServerWindows::screen_get_usable_rect(int p_screen) const {