lxdrgen-cpp: add a Qt backend

Motivation: some Android NDKs do not have iconv.

tools/lxdrgen-cpp-qt.cpp

@@ -0,0 +1,23 @@
+// lxdrgen-cpp-qt.cpp: Qt support code for lxdrgen-cpp.awk.
+//
+// Copyright (c) 2024, Přemysl Eric Janouch <p@janouch.name>
+// SPDX-License-Identifier: 0BSD
+#include <QString>
+#include <string>
+
+namespace LibertyXDR {
+
+bool utf8_to_wstring(const uint8_t *utf8, size_t length, std::wstring &wide) {
+	QByteArrayView view(reinterpret_cast<const char *>(utf8), length);
+	if (!view.isValidUtf8())
+		return false;
+	wide = QString::fromUtf8(view).toStdWString();
+	return true;
+}
+
+bool wstring_to_utf8(const std::wstring &wide, std::string &utf8) {
+	utf8 = QString::fromStdWString(wide).toUtf8().toStdString();
+	return true;
+}
+
+} // namespace LibertyXDR