LibJS: Make ASTNode::generate_bytecode() fallible

Instead of crashing on the spot, return a descriptive error that will
eventually continue its days as a javascript "InternalError" exception.
This should make random crashes with BC less likely.

Userland/Libraries/LibJS/Bytecode/CodeGenerationError.h

@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2022, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Error.h>
+#include <AK/StringView.h>
+#include <LibJS/Forward.h>
+
+namespace JS::Bytecode {
+
+struct CodeGenerationError {
+    ASTNode const* failing_node { nullptr };
+    StringView reason_literal;
+
+    String to_string();
+};
+
+template<typename T>
+using CodeGenerationErrorOr = ErrorOr<T, CodeGenerationError>;
+
+}