Fix bug #12082 with input of Meta-non-ASCII-characters on MS-Windows.

Fix bug #12082 with input of Meta-non-ASCII-characters on MS-Windows.

 src/w32fns.c (w32_wnd_proc): Pass w32_keyboard_codepage to
 w32_kbd_patch_key as the 2nd arg.
 src/w32term.c <w32_keyboard_codepage>: Renamed from
 keyboard_codepage and now external.  All users changed.
 src/w32term.h: Add declaration of w32_keyboard_codepage.
 src/w32inevt.c (w32_kbd_patch_key): Accept an additional argument --
 the codepage to translate keys to Unicode.  If this argument is
 -1, use the value returned by GetConsoleCP.  All callers changed.