[6.x] Better collapsible sections

[jaygeorge]

Description of the Problem

As described in #14488 collapse / expand sections can feel a bit off when animating.

This is basically because we're using overflow: clip; to hide the inside container, and this is not controlled with an animation.
Instead, it relies on a basic height transition on the container and clipped contents – which is why it feels like it "plops" on to the page when expanding.

What this PR Does

• Adds some animation keyframes so we have better control of how the overclip and animation works.
• Takes into consideration motion preferences.
• I've opted into the animation when hovering over data-ui-panel, so things don't animate when the page loads
• Closes Expand section animation is slower than fields showing #14488

Before

2026-05-15.at.14.42.25.mp4

After

2026-05-15.at.14.41.26.mp4

How to Reproduce

1. Make a section collapsible and toggle its state