QmlDesigner: Create thumbnail for imported 3D assets

Qmlpuppet now allows creating icon from qml source code.

Invoke qmlpuppet with following arguments to create icons:
--rendericon <size> <icon file name> <icon qml source>

E.g. --rendericon 24 ~/my_icon.png ~/my_icon.qml

Two icons are created, one with size x size dimensions and
one with double the dimensions and "@2x" injected into the file name.

3D asset import utilizes this icon rendering to produce item library
icons for imported components.

Change-Id: I92c62c80d961f5f61a0ce1c09b32bbcbf80ea56c
Fixes: QDS-1052
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

share/qtcreator/qml/qmlpuppet/qml2puppet/iconrenderer/iconrenderer.h

@@ -0,0 +1,56 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include <QtCore/qobject.h>
+#include <QtCore/qstring.h>
+
+#include <designersupportdelegate.h>
+
+QT_BEGIN_NAMESPACE
+class QQuickView;
+class QQuickItem;
+QT_END_NAMESPACE
+
+class IconRenderer : public QObject
+{
+    Q_OBJECT
+
+public:
+    explicit IconRenderer(int size, const QString &filePath, const QString &source);
+
+    void setupRender();
+
+private:
+    void render(const QString &fileName);
+
+    int m_size = 16;
+    QString m_filePath;
+    QString m_source;
+    QQuickView *m_quickView = nullptr;
+    QQuickItem *m_contentItem = nullptr;
+    DesignerSupport m_designerSupport;
+};