#266 breaks DPI awareness for `open_blocking` windows

[AlexCharlton]

I'm not yet sure why, but #266 seems to have stopped windows created with open_blocking from fetching the right resolution. The window.get_dpi call in after_create is always returning the default 96, regardless of the scale of my screen. Calling get_dpi later on (manually triggering in a click event handler) continues to return 96.

[AlexCharlton]

After some experimentation, I've found that this relates to the DpiAwarenessContext getting dropped before window creation. Creating a new DpiAwarenessContext in create_window will open a window with the right resolution, and doesn't seem to have any deleterious effects in a parented context:

pub fn create_window<W: WindowImpl>(
    title: &HSTRING, style: WindowStyle, nc_size: PhySize, parent: HWND,
    initializer: impl FnOnce(HWnd) -> W + 'static,
) -> Result<HWND> {
    let instance = HInstance::get();
    let window_class = RegisteredClass::register_new(instance, Some(wnd_proc::<W>))?;

    let data = WindowData::new(initializer, window_class.clone());

    let extended_user_32 = super::ExtendedUser32::load().unwrap();
    let _dpi_ctx = super::DpiAwarenessContext::new(&extended_user_32).unwrap();

    let hwnd = unsafe {
        CreateWindowExW(
            style.style_ex,
            window_class.as_atom_ptr(),
            title.as_ptr(),
            style.style,
            0,
            0,
            nc_size.width.try_into().unwrap_or(i32::MAX),
            nc_size.height.try_into().unwrap_or(i32::MAX),
            parent,
            null_mut(),
            instance.as_raw(),
            Rc::into_raw(data).cast(),
        )
    };

    if hwnd.is_null() {
        return Err(Error::from_win32());
    }

    Ok(hwnd)
}

Creating the context any later (like in initialize/after_create) does not have any effect.

@prokopyl, not sure if you think this is the right place to do this, though. If so, I can open a PR.