Allow keyboard navigation to be toggled at runtime

Hello,

I was wondering if it would be possible to allow the "keyboard navigation" feature in Qt Virtual Keyboard to be something that could be toggled at runtime. Currently it is exposed under a build flag: -vkb-arrow-keynavigation

qt-virtualkeyboard is packaged in different Linux distributions that have the default build flags. We are currently building a qt-vkbd based project that needs keyboard navigation, and rely on a hack (emitting navigationKeyReleased from qvirtualkeyboardinputcontext_p.h): https://invent.kde.org/plasma/plasma-keyboard/-/merge_requests/25