This patch adds two properties to QML type CameraFocus,
to gain feature parity with the C++ interface of QCameraFocus.
Additionally, it deprecates the older, comparable functions.

Task-number: QTBUG-45336
Change-Id: Iffc5c805409ed605dba5d4bc3fa2f05122b58b9e
Reviewed-by: Christian Stromme <christian.stromme@qt.io>