(PUP-836) FFI Puppet::Util::Windows::User

 - LogonUserW, LoadUserProfile, UnloadUserProfile and PROFILEINFO
   have been converted from manually packing params with Win32API.new to
   automatically managed with FFI definitions.
 - Use MemoryPointer where appropriate.
 - To use Puppet::Util::Windows::String as a mix-in, must be included
   earlier in util/windows.rb.
 - Note that wide character LogonUserW is used rather than platform
   varying LogonUser as FFI is unable to use that.  The pointer
   widths of PROFILEINFO vary depending on platform, which is handled
   by using :pointer.  With LogonUserW the string pointed to is always
   wide character, which is properly handled by using wide_string.
(PUP-836) FFI Puppet::Util::Windows::User

 - Remove dependence on Win32 API calls defined in the win32-security
   gem, including CreateWellKnownSid, IsValidSid, CheckTokenMembership
 - These calls have all been FFI'd accordingly
(PUP-836) Remove Win32::Security.elevated_security

 - Refactor Puppet::Util::Windows::Process to implement new method
   elevated_security? that was in win32-security gem
 - Refactor get_token_information to return an FFI::MemoryPointer buffer
   instead of a parsed structure, since GetTokenInformation is a generic
   call that can return many structure types, including TOKEN_ELEVATION.
 - Remove any reliance on win32-security gem from user.rb
 - Adjust tests accordingly