[List vNext] Add animation to expand/collapse trigger

[sophialee0416]

Platforms Impacted

• iOS
• macOS

Description of changes

List expand/collapse did not have an animation when triggered externally. This fix changes that so the list is able to animate expand/collapse smoothly.

Verification

Before	After

Pull request checklist

This PR has considered:

• Light and Dark appearances
• VoiceOver and Keyboard Accessibility
• Internationalization and Right to Left layouts
• Different resolutions (1x, 2x, 3x)
• Size classes and window sizes (iPhone vs iPad, notched devices, multitasking, different window sizes, etc)

Microsoft Reviewers: Open in CodeFlow

[mischreiber]

Couple thoughts from the animation:

• It looks like the list of status items are still disappearing without animation, even though the list is collapsing smoothly. It's definitely an improvement, but not quite as complete as the expand animation (where the status items fade in from 0). Anything we can do about that?
• If you watch closely when "Busy" becomes "Available", you can see that the frame for the "Available" text is animating too, giving the impression that it's writing the word character by character. Can we suppress that part of the animation?

Overall I think it's an improvement over what we currently have, but if we can make these two additional changes then it'll be flawless.

[sophialee0416]

Couple thoughts from the animation:

• It looks like the list of status items are still disappearing without animation, even though the list is collapsing smoothly. It's definitely an improvement, but not quite as complete as the expand animation (where the status items fade in from 0). Anything we can do about that?
• If you watch closely when "Busy" becomes "Available", you can see that the frame for the "Available" text is animating too, giving the impression that it's writing the word character by character. Can we suppress that part of the animation?

Overall I think it's an improvement over what we currently have, but if we can make these two additional changes then it'll be flawless.

Good eye! Thanks for the catch. I will look into that further!