Animated checkbox and radio button tick transitions (implemented on a fork)

[xqsit94]

I added some animation to the checkbox and radio button. Since you're not accepting pull requests right now, I've implemented it on my fork instead — I respect that, so opening this as an issue in case it's useful.

Previous

Now:

What changed

• Checkbox — checking it now animates: the border thickens inwards until it fills the box, then the tick strokes itself on. Unchecking plays it in reverse. Previously it swapped between the two states instantly.
• Radio button — same fill-inwards transition, with the inner dot popping in.
• Labels are clickable — clicking the text next to a checkbox or radio button now toggles it, instead of only the box itself being a hit target.

Branch: https://github.com/xqsit94/infinipaint/tree/checkbox-radio-improvements
Commit: xqsit94@0e3b8e2

I'd be interested in contributing more — happy to work in whatever way suits you best once the code settles down.