added additional easing functions

[fjkorf]

Objective

Fixes #17744

Solution

This updated adds three additional easing functions to support the full set of functions available in CSS
https://developer.mozilla.org/en-US/docs/Web/CSS/easing-function/steps#description

Three new EaseFunctions were added, and the original EaseFunction::Steps was modified.

I thought it made the most sense to have Steps be equivalent to jump-none, and added additional functions for the remaining options. StepsStart for jump-start, and so on. The original Steps function is now StepsEnd, which may be a problem .

Testing

I updated the EaseFunctions example to include the three new functions, and successfully tested the code locally.

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Showcase

Migration Guide

Calls to EaseFunction::Steps would need to be updated to EaseFunction::StepsEnd to display the same behavior

[alice-i-cecile]

@greeble-dev can I get your review here? :)

[alice-i-cecile]

This feels both clearer and more consistent with CSS to add an enum and specify this behavior inside of the existing Steps variant. That will also make the migration easier and more automatic.

[greeble-dev]

Awkward.... I think this PR and #17752 both implement the same feature.

#17752 has the advantage of addressing @alice-i-cecile 's comment about making the jump behaviour an enum, and includes updated svgs. But this PR is a bit simpler - the other adds a StepConfig intermediate struct that makes things a bit verbose.

let c = EasingCurve::new(2.0, 4.0, EaseFunction::Steps(StepConfig::new(4).with_jump_at(JumpAt::Start)));

I'd be happy to review either PR in more detail, but I'm reluctant to do that with both in play.

[greeble-dev]

Although I'll walk that back slightly - if a maintainer says "I'd rather you review both PRs and then we'll see what happens" then I can do that.

[alice-i-cecile]

Let's coalesce the efforts in #17752 :)