Element.scrollTop sometimes should be decimal

[cardenaso11]

Element.scrollTop is given a 'long' type in the webIDL, but in actuality it can become fractional when display scaling comes into play, according to https://developer.mozilla.org/en-US/docs/Web/API/Element/scrollTop & in practice, & then it's rounded

This comes up in the generated Haskell code as a rounded Int