Avoid fractional scroll position impacting current index. (#25877)
Avoid fractional scroll position impacting current index. (#25877)

- Use center alignment for slides in carousel 0.2, avoiding an issue
with fractional scroll positions not being tracked. While fractional
scroll is being fixed in Chrome, it may take longer to land in Safari.
zhouyx/amphtml,zhouyx/amphtml,rsimha-amp/amphtml,alanorozco/amphtml,jridgewell/amphtml,nexxtv/amphtml,media-net/amphtml,adup-tech/amphtml,mhc-gh/amphtml,smartadserver/amphtml,honeybadgerdontcare/amphtml,yandex-pcode/amphtml,tlong2/amphtml,nexxtv/amphtml,tlong2/amphtml,voyagegroup/amphtml,media-net/amphtml,taboola/amphtml,lannka/amphtml,media-net/amphtml,smartadserver/amphtml,erwinmombay/amphtml,sharethrough/amphtml,voyagegroup/amphtml,prateekbh/amphtml,alanorozco/amphtml,jmadler/amphtml,Gregable/amphtml,rsimha-amp/amphtml,zhouyx/amphtml,ampproject/amphtml,Gregable/amphtml,cory-work/amphtml,taboola/amphtml,nexxtv/amphtml,nexxtv/amphtml,sharethrough/amphtml,tlong2/amphtml,prateekbh/amphtml,danielrozenberg/amphtml,cory-work/amphtml,mhc-gh/amphtml,zhouyx/amphtml,honeybadgerdontcare/amphtml,honeybadgerdontcare/amphtml,sharethrough/amphtml,lannka/amphtml,jpettitt/amphtml,danielrozenberg/amphtml,zhouyx/amphtml,jmadler/amphtml,alanorozco/amphtml,tlong2/amphtml,tlong2/amphtml,erwinmombay/amphtml,media-net/amphtml,danielrozenberg/amphtml,voyagegroup/amphtml,taboola/amphtml,adup-tech/amphtml,mhc-gh/amphtml,sharethrough/amphtml,yandex-pcode/amphtml,cory-work/amphtml,prateekbh/amphtml,danielrozenberg/amphtml,ampproject/amphtml,erwinmombay/amphtml,voyagegroup/amphtml,jmadler/amphtml,yandex-pcode/amphtml,sharethrough/amphtml,mhc-gh/amphtml,jmadler/amphtml,cory-work/amphtml,erwinmombay/amphtml,taboola/amphtml,mhc-gh/amphtml,danielrozenberg/amphtml,yandex-pcode/amphtml,prateekbh/amphtml,jridgewell/amphtml,src-code/amphtml,jpettitt/amphtml,danielrozenberg/amphtml,jridgewell/amphtml,jridgewell/amphtml,tlong2/amphtml,rsimha-amp/amphtml,jmadler/amphtml,src-code/amphtml,sharethrough/amphtml,adup-tech/amphtml,adup-tech/amphtml,erwinmombay/amphtml,voyagegroup/amphtml,nexxtv/amphtml,alanorozco/amphtml,jmadler/amphtml,rsimha-amp/amphtml,danielrozenberg/amphtml,Gregable/amphtml,rsimha-amp/amphtml,ampproject/amphtml,smartadserver/amphtml,zhouyx/amphtml,smartadserver/amphtml,jridgewell/amphtml,smartadserver/amphtml,lannka/amphtml,yandex-pcode/amphtml,alanorozco/amphtml,ampproject/amphtml,lannka/amphtml,prateekbh/amphtml,honeybadgerdontcare/amphtml,media-net/amphtml,ampproject/amphtml,jridgewell/amphtml,media-net/amphtml,taboola/amphtml,rsimha-amp/amphtml,prateekbh/amphtml,adup-tech/amphtml,mhc-gh/amphtml,cory-work/amphtml,jpettitt/amphtml,jpettitt/amphtml,Gregable/amphtml,Gregable/amphtml,smartadserver/amphtml,nexxtv/amphtml,src-code/amphtml,cory-work/amphtml,ampproject/amphtml,jpettitt/amphtml,voyagegroup/amphtml,yandex-pcode/amphtml,danielrozenberg/amphtml,voyagegroup/amphtml,zhouyx/amphtml,adup-tech/amphtml,yandex-pcode/amphtml,jridgewell/amphtml,honeybadgerdontcare/amphtml,jpettitt/amphtml,nexxtv/amphtml,prateekbh/amphtml,Gregable/amphtml,mhc-gh/amphtml,rsimha-amp/amphtml,src-code/amphtml,src-code/amphtml,alanorozco/amphtml,jpettitt/amphtml,jpettitt/amphtml,src-code/amphtml,ampproject/amphtml,lannka/amphtml,honeybadgerdontcare/amphtml,Gregable/amphtml,taboola/amphtml,Gregable/amphtml,erwinmombay/amphtml,taboola/amphtml,media-net/amphtml,honeybadgerdontcare/amphtml,lannka/amphtml,cory-work/amphtml,alanorozco/amphtml,alanorozco/amphtml,ampproject/amphtml,mhc-gh/amphtml,lannka/amphtml,media-net/amphtml