[LLDB/Lua] call lua_close() on Lua dtor

[tammela]

Summary

This patch calls lua_close() on Lua dtor.

This guarantees that the Lua GC finalizers are honored, aside from the
usual internal clean up.

It also guarantees a call to the __close metamethod of any active
to-be-closed variable in Lua 5.4.

Since the previous luaL_openlibs() was a noop, because the standard
library is cached internally, I've removed it.

[JDevlieghere]

Thanks!

lldb/source/Plugins/ScriptInterpreter/Lua/Lua.h

public:
   Lua() : m_lua_state(luaL_newstate()) {
     assert(m_lua_state);
     luaL_openlibs(m_lua_state);
     luaopen_lldb(m_lua_state);
   }
 
   ~Lua() {
     assert(m_lua_state);
-    luaL_openlibs(m_lua_state);
+    lua_close(m_lua_state);
   }
 
   llvm::Error Run(llvm::StringRef buffer);
   llvm::Error LoadModule(llvm::StringRef filename);
   llvm::Error ChangeIO(FILE *out, FILE *err);
 
 private:
   lua_State *m_lua_state;
 };
 
 } // namespace lldb_private
 
 #endif // liblldb_Lua_h_