### Godot version

4.0.beta12

### System information

Windows 11, RTX 3080

### Issue description

When a Window Node is created with it's Transparent flag set to true and Project Settings --> Display --> Window --> Subwindows --> Embed Subwindows is false, the Window has a black background. By cycling the transparent flag from false and back to true again, during runtime, the window's background then becomes transparent. 

### Steps to reproduce

Attempt to create a Non-embedded Subwindow with a transparent background using the appropriate flags. 

### Minimal reproduction project

Note: this project is from Reddit user [gongpha](https://www.reddit.com/user/gongpha/) and his Reddit post [Learning a Godot 4.0 Window node](https://www.reddit.com/r/godot/comments/xr8yxn/learning_a_godot_40_window_node/)

https://github.com/gongpha/godot4-window-test
for (int i = 0; i < fcount; i++) {
				DragQueryFileW(hDropInfo, i, buf, buffsize);
				String file = String::utf16((const char16_t *)buf);
				files.push_back(file);
			}
			if (files.size() && !windows[window_id].drop_files_callback.is_null()) {
				Variant v = files;
				Variant *vp = &v;
				Variant ret;
				Callable::CallError ce;
				windows[window_id].drop_files_callback.callp((const Variant **)&vp, 1, ret, ce);
			}
		} break;
		default: {
			if (user_proc) {
				return CallWindowProcW(user_proc, hWnd, uMsg, wParam, lParam);
			}
		}
	}
	return DefWindowProcW(hWnd, uMsg, wParam, lParam);
}
LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam) {
	DisplayServerWindows *ds_win = static_cast<DisplayServerWindows *>(DisplayServer::get_singleton());
	if (ds_win) {
		return ds_win->WndProc(hWnd, uMsg, wParam, lParam);
	} else {
		return DefWindowProcW(hWnd, uMsg, wParam, lParam);
	}
}
void DisplayServerWindows::_process_activate_event(WindowID p_window_id, WPARAM wParam, LPARAM lParam) {