Provide overscroll flag in scroll event

### Problem description

`ScrollView` and `CollectionView` overscroll on iOS when pulling content beyond the min/max scroll position and bounce-back when letting go. Overscroll and bounce-back behaviors often need to be ignored when applying a translation dependent on `"scroll"` events.

It is possible to check whether a `"scroll"` event has been fired during overscroll by accumulating scroll deltas and comparing accumulated value with max/min possible offset. However, this is not very convenient, since calculating the max offset requires calculating the overall width/height of the scrollable content as well.

### Expected behavior

Provide a boolean property in the `"scroll"` event, which indicates whether this event has been fired during overscroll.

### Environment

- Tabris.js version: 3.x