[BREAKING CHANGE] SelectWidget: Remove getHighlightedItem
[BREAKING CHANGE] SelectWidget: Remove getHighlightedItem

Follows-up on I7213476574a62e54e05d4ffa8539b2f881acb214

Bug: T76630
Change-Id: I6c8abad099e299bd40a13e6ce9eba5c6432b939b

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui