Support more "step" easing modes

[rparrett]

I think it would be good to support all of the CSS modi of steps via configuration options somewhere. Can you open an issue and link to this PR please? I'll tackle it later on when I'm back home (on mobile atm)

Originally posted by @RobWalt in #17743 (review)

See https://developer.mozilla.org/en-US/docs/Web/CSS/easing-function/steps#description.

After #17743, our Step easing will be like "jump-end" (the default) in CSS, but it would be nice to support other modes.