arraysDiffSequence computes the ordered operations needed to transform an old array into a new array. In virtual-DOM reconciliation, those operations later drive child-node updates without rebuilding every unchanged child. section 7.6.4 section 8.5
A small transformation
For oldArray = ['a', 'b'] and newArray = ['b', 'c'], the current position first becomes a move for 'b', then an addition for 'c'; remaining unmatched items are removed when necessary. String arrays use the default === comparator, while virtual-node objects require a custom equalsFn. section 7.6.4
