message: Introduce Strings::EMPTY
diff: @@ -36,6 +36,9 @@ namespace vcpkg::Strings::details
  namespace vcpkg::Strings
  {
  + static constexpr const CStringView EMPTY = "";
  + static constexpr const CWStringView WEMPTY = L"";
  +
  template<class... Args>
  std::string format(const char* fmtstr, const Args&... args)
  {
  