Investigate and implement accessibility improvements for `RangeInput`

[dpikt]

Looks like there might be some enhancements we can make: https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/ARIA_Techniques/Using_the_slider_role

[chawes13]

It looks like we're also using a label element for the range, which looks like output might be the most appropriate (although it's not supported by IE11).

https://caniuse.com/?search=output

ARIA Authoring Practices just uses a div for the value