[NUI][AT-SPI] Fix accessibility activation for RecyclerViewItem

[NUI][AT-SPI] Fix accessibility activation for RecyclerViewItem

Because the implementation of RecyclerViewItem.OnAccessibilityActivated
would look identical to Button.OnAccessibilityActivated, to avoid code
duplication, accessibility activation is reimplemented in terms of
OnKeyboardEnter for all controls, just like it is done in DALi.