video/windows: ANSI/UNICODE updates (cf. bug 5435): - explicitly use UNICODE versions of DrawText, EnumDisplaySettings, EnumDisplayDevices, and CreateDC: the underlying structures have WCHAR strings. - change WIN_UpdateDisplayMode and WIN_GetDisplayMode() to accept LPCWSTR instead of LPCTSTR for the same reason. - change WIN_StringToUTF8 and WIN_UTF8ToString to the explicit 'W' versions where appropriate.