GF-61350: Prevent using outdated scroll position when scroller size changes.

Issue
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For `ExpandableInputPickerSample`, the `ScrollThumb` appears below the bottom arrow when the picker is closed.

Fix
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When we call `setupBounds` in the `requestScrollIntoView` handler, the scroll position is synced via a `scrollTo` call in `clampScrollPosition`. In the subsequent `animateToControl` call, the getter `getScrollBounds` actually stops the scroll via a `stop` call. We now use the `_getScrollBounds` call instead, which does not issue a `stop` call.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>