Implement focus and text caret tracking in the zoom effect

The zoom effect provides a focus tracking feature. The problem with it is that it depends on kaccessibleapp, which seems to be dead.

There is a library called libqaccessibilityclient that one could use for the accessibility purposes, e.g. tracking focus changes or text caret movements.

This merge request ports the zoom effect from kaccessibleapp's d-bus api to libqaccessibleclient to fix the focus tracking feature and implement text caret tracking.

In case libqaccessibilityclient is not installed, the accessibility features in the zoom effect will be disabled and relevant ui options won't be shown in the kcm.