nearestAccessibilityClickable

The innermost element on this hit path that is clickable, or null if none is.

autograph-compose attributes a tap this way. The native pipeline reached the same answer through this function until #191, and now reaches it along a hitTest chain instead (resolveNativeTapTargetByHitTest, whose leaf-upward search is deliberately the same shape) — the two must still agree, or a hybrid app reports one button under two names. Searching from the leaf upward is what makes a button inside a tappable row attribute to the button rather than the row.

This lives here, next to the predicate it applies, so that agreement is a single definition rather than two call sites that happen to be written identically. The clickability predicate is expected to change — isAccessibilityButton is deliberately narrow, and the documented .onTapGesture-on- Text gap would be closed by widening it — and a widening applied to one copy only would silently split the two pipelines apart.

Expects the path in root-to-leaf order, as deepestAccessibilityHitPath returns it.