(PUP-2382) FFI typedef for win32_bool / fix User

• Previously check_token_membership was failing in 2003 spec tests due to 2 issues
  • FFI::Pointer::NULL cannot be used in place of our :handle typedef, and therefore we must add a new constant of 0 to be used for NULL handles
  • FFI defines a :bool as variable width "(?? 1 byte in C++)", while Win32 defines a BOOL as int, and is fixed to 4 bytes on x86 and x64
• Fortunately the bool issue really only bit us in the one spot where we were using a pointer to a bool, but by adding a new typedef for :win32_bool, all call sites comparing the return value needed to be updated for correctness to compare against FFI::WIN32_FALSE
• A test was added to ensure these APIs are called during spec tests on all Windows platforms, and not just 2003