Move QObjectBindableProperty documentation into snippet file

The \Q_OBJECT macro has been removed but using Q_OBJECT in the file
would erroneously trigger automoc. Avoid the issue by moving
the snippet into its own file.

Task-number: QTBUG-89505
Pick-to: 6.0
Change-Id: I6630ff4bfcbf33eae348ac3d92aae1878dc573ea
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

src/corelib/doc/snippets/code/src_corelib_kernel_qproperty.cpp

@@ -0,0 +1,70 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** 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.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QObject>
+
+//! [0]
+class MyClass : public QObject
+{
+    Q_OBJECT
+    Q_PROPERTY(int x READ x WRITE setX NOTIFY xChanged BINDABLE bindableX)
+public:
+    int x() const { return xProp; }
+    void setX(int x) { xProp = x; }
+    QBindable<int> bindableX() { return QBindable<int>(&xProp); }
+
+signals:
+    void xChanged();
+
+private:
+    // Declare the instance of the bindable property data.
+    Q_OBJECT_BINDABLE_PROPERTY(MyClass, int, xProp, &MyClass::xChanged)
+};
+//! [0]

src/corelib/kernel/qproperty.cpp

@@ -944,24 +944,7 @@ QString QPropertyBindingError::description() const
 
   Use the Q_BINDABLE_PROPERTY macro in the class declaration to declare the property as bindable.
 
-  \code
-    class MyClass : public QObject
-    {
-        \Q_OBJECT
-        Q_PROPERTY(int x READ x WRITE setX NOTIFY xChanged BINDABLE bindableX)
-    public:
-        int x() const { return xProp; }
-        void setX(int x) { xProp = x; }
-        Bindable<int> bindableX() { return QBindable<int>(&xProp); }
-
-    signals:
-        void xChanged();
-
-    private:
-        // Declare the instance of the bindable property data.
-        Q_OBJECT_BINDABLE_PROPERTY(MyClass, int, xProp, &MyClass::xChanged)
-    };
-  \endcode
+  \snippet code/src_corelib_kernel_qproperty.cpp 0
 
   If the property does not need a changed notification, you can leave out the "NOFITY xChanged" in the Q_PROPERTY macro as well as the last argument
   of the Q_OBJECT_BINDABLE_PROPERTY macro.