LibJS: Allow reserved words as keys in object expressions.

Author: https://github.com/sunverwerth
Commit: bf5b251684
Pull-request: https://github.com/SerenityOS/serenity/pull/1849
Issue: https://github.com/SerenityOS/serenity/issues/1768

Libraries/LibJS/Parser.h

@@ -84,6 +84,7 @@ private:
     bool match_secondary_expression() const;
     bool match_statement() const;
     bool match_variable_declaration() const;
+    bool match_identifier_name() const;
     bool match(TokenType type) const;
     bool done() const;
     void expected(const char* what);