[BREAKING CHANGE] SelectWidget: Remove getSelectedItem
[BREAKING CHANGE] SelectWidget: Remove getSelectedItem

Follows-up on I0f1d9c1f31efcc10d3647103548770d2101050d9

Bug: T76630
Change-Id: I8ffeb402c73a989fc8814c51cff4015fea450a8b

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