LibJS: Disallow 'with' statement in strict mode

Author: https://github.com/linusg
Commit: 3ac7fb9f6c
Pull-request: https://github.com/SerenityOS/serenity/pull/4205

Libraries/LibJS/Parser.cpp

@@ -328,6 +328,8 @@ NonnullRefPtr<Statement> Parser::parse_statement()
     case TokenType::While:
         return parse_while_statement();
     case TokenType::With:
+        if (m_parser_state.m_strict_mode)
+            syntax_error("'with' statement not allowed in strict mode");
         return parse_with_statement();
     case TokenType::Debugger:
         return parse_debugger_statement();