BHV-16979: New IntegerPicker doesn't ensure consistent width while scrolling

### Issue:
- IntegerPicker width is decided by the digit length of number.
- But, each character has different width on font.

### Fix:
Add a invisible buffer that occupies some fixed width.

DCO-1.1-Signed-Off-By: Kunmyon Choi kunmyon.choi@lge.com
If we're only ever passing in `this.value` to `setupBuffer`, I think we can eliminate this parameter and just access `this.value` directly in this method.