Provide and document a proper replacement for InputContext.inputItem

InputContext.inputItem was silently removed then restored in Qt 5.12 (see QTBUG-72494 ). However,

• Our documentation simply marks it as "deprecated", without specifying how to replace it: https://doc.qt.io/qt-6/qml-qtquick-virtualkeyboard-inputcontext-obsolete.html#inputItem-prop
• Our official example still uses a private "alias" of that property: (https://github.com/qt/qtvirtualkeyboard/blob/v6.8.0/examples/virtualkeyboard/basic/content/AutoScroller.qml#L11 ):

The value of this property seems to correspond to QGuiApplication::focusObject. However, that is not exposed to QML (https://doc.qt.io/qt-6/qml-qtquick-application.html does not contain Application.focusObject)

Suggestions

1. Provide new QML API and/or identify an existing QML API to replace InputContext.inputItem
2. Make https://doc.qt.io/qt-6/qml-qtquick-virtualkeyboard-inputcontext-obsolete.html#inputItem-prop point to that API
3. Update https://github.com/qt/qtvirtualkeyboard/blob/v6.8.0/examples/virtualkeyboard/basic/content/AutoScroller.qml to use that new API