fix(scroll): correct inverted list rendering and wheel direction on web

[HuuNguyen312]

Description

Fixes inverted list rendering and mouse-wheel direction on web (e.g. Electron). Native is unaffected.

On web, inverted lists are flipped with transform: scaleY(-1) (scaleX(-1) when horizontal). This broke two things:

1. Rendering froze (~20 items, then blank)

measureFirstChildLayout read mirrored getBoundingClientRect coordinates, so firstItemOffset grew with scroll instead of staying ~0. The internal scrollOffset (y - firstItemOffset) went negative → getVisibleLayouts clamped to index 0 → the engaged index froze → renderItem stopped being called while scrolling.

Fix: detect the scaleY(-1) transform and measure from the bottom edge when flipped, so firstItemOffset stays ~0 (matching non-inverted).

2. Mouse wheel scrolled the wrong way

The native wheel delta is not flipped by the container transform, so it scrolled opposite to the content.

Fix: a web-only useInvertedWheelFix hook re-inverts the wheel delta on the scroll node (-= deltaY, or -= deltaX when horizontal). Setting scrollTop / scrollLeft still fires the scroll event, so virtualization keeps working.

Native behavior is unchanged — measureLayout.ts and the native hook variant (useInvertedWheelFix.ts) are no-ops / untouched.

Affected package: @shopify/flash-list

Changed files

File	Change
src/recyclerview/utils/measureLayout.web.ts	add isVerticallyFlipped, measure from bottom when flipped
src/recyclerview/hooks/useInvertedWheelFix.web.ts	web wheel re-invert (new)
src/recyclerview/hooks/useInvertedWheelFix.ts	native no-op (new)
src/recyclerview/RecyclerView.tsx	wire up the hook

Reviewers' hat-rack 🎩

• Web, inverted list — scroll up/down keeps rendering items (no blank area), wheel scrolls in the correct direction
• Native (iOS/Android), inverted list — no behavior change; smooth scroll, renderItem fires as expected
• firstItemOffset stays ~0 while scrolling an inverted list on web (was growing 1057 → 4009 → 9923 before the fix)