Fix bug #10299 with Unicode characters sent on MS-Windows by MSKLC.

Fix bug #10299 with Unicode characters sent on MS-Windows by MSKLC.

 src/w32fns.c (INIT_WINDOW_CLASS): New macro.
 (w32_init_class): Use it to initialize the Emacs class with either
 ANSI or Unicode API calls.
 (w32_msg_pump): Call GetMessageW and DispatchMessageW on NT and
 later.
 (w32_wnd_proc): If the character code sent by WM_CHAR or
 WM_SYSCHAR is above 255, post a WM_UNICHAR message, not the
 original message.  Call DefWindowProcW on NT and later.