LibJS: Don't create arguments object due to o.arguments access

When deciding whether we need to create a full-blown `arguments` object,
we look at various things, starting as early as in the parser.

Until now, if the parser saw the identifier `arguments`, we'd decide
that it's enough of a clue that we should create the `arguments` object
since somebody is obviously accessing it.

However, that missed the case where someone is just accessing a property
named `arguments` on some object. In such cases (`o.arguments`), we now
hold off on creating an `arguments` object.

~11% speed-up on Octane/typescript.js :^)

Userland/Libraries/LibJS/Parser.h

@@ -305,6 +305,7 @@ private:
     struct ParserState {
         Lexer lexer;
         Token current_token;
+        bool previous_token_was_period { false };
         Vector<ParserError> errors;
         ScopePusher* current_scope_pusher { nullptr };