luaengine: reduce memory usage during compilation

Previous semantics were encouraged by sol2, and ThePhD admitted it was a bad idea for usertypes with lots of members. sol3 allows to assign members outside a constructor for regular usertypes, but mame can't move to sol3 because it requires C++17. Turns out sol2 also has a way to add members separately, and that is what I used. This helps immensely.

This approach required a fix to warning C5046 copied from here 5799084572

Tested current mame plugins, everything seems to work.

PS: Due to come black magic, if I use simple_usertype::set() with "manager" as well, "machine" member dies (others are fine!), so I had to leave it intact.

3rdparty/sol2/sol/traits.hpp

@@ -252,7 +252,7 @@ namespace sol {
 				using yes = char;
 				using no = struct { char s[2]; };
 
-				struct F { void operator()(); };
+				struct F { void operator()() {}; };
 				struct Derived : T, F {};
 				template<typename U, U> struct Check;