Create Default IME window and register it

The default IME window is a special window of window class "IME" and of window text "Default IME".

We have to create the default IME window for each top-level non-IME window creation.
imm32!ImmGetDefaultIMEWnd should return the handle of the default IME window that is associated to the specified window.

In Wine, imm32!__wine_register_window creates the default IME window.