iOS: Extract basic devicectl output processing

Put creating the JSON document and error parsing into a separate
function.

Change-Id: I257f82249a07220467c33220c6b8e4650266b8d9
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/plugins/ios/devicectlutils.h

@@ -0,0 +1,14 @@
+// Copyright (C) 2024 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+#pragma once
+
+#include <utils/expected.h>
+
+#include <QJsonValue>
+
+namespace Ios::Internal {
+
+Utils::expected_str<QJsonValue> parseDevicectlResult(const QByteArray &rawOutput);
+
+} // namespace Ios::Internal