BHV-15753: Refresh scroll bounds upon entering scroller.

### Issue
We had previously made an optimization to the `enter` handler to remove unnecessary calls, and as a result the scroll bounds were not being refreshed as necessary, resulting in the paging controls not always having the correct enabled/disabled state. This is partly related to `moon.DataList`not rendering its contents immediately, as in the initial bounds are incorrect.

### Fix
Technically, the previous call to `setThumbSizeRatio` method was calling `_getScrollBounds`, so we call that directly here.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>