fix(inverted): force firstItemOffset to 0 for inverted lists

[VickyStash]

Description

Problem

Inverted FlashList only renders a few items, leaving the rest of the viewport as white space while scrolling.

RecyclerView measures firstItemOffset by calling measureFirstChildLayout relative to the outer container. When inverted is true, the outer container has a scaleY: -1 transform applied, which flips the coordinate system. As a result, the measured y-offset comes back equal to the container height instead of 0.

That bad offset propagates through adjustedOffset = scrollOffset - firstItemOffset, pushing every adjusted scroll position into negative space where no items live.
Only the handful of items caught by the draw-distance buffer ever render — everything else stays blank.

Reproduction stack: https://snack.expo.dev/@vikstash/inverted-flashlist-bug

Steps:

1. Open an inverted list with 50 items.
2. Scroll to top.
3. See the 35th+ items are not rendered at all, and blank space displays.

Bug video:

fl-bug.mp4

Solution

Force firstItemOffset to 0 when inverted is true. The scaleY: -1 transform already handles the visual inversion, so the raw offset measured against the flipped coordinate system isn't needed (and is actively wrong).

Reviewers’ hat-rack 🎩

• Render an inverted FlashList and confirm the full viewport is filled with items (not just the draw-distance buffer)
• Verify a non-inverted vertical FlashList still renders and scrolls correctly (no regression to the default path)

[VickyStash]

@naqvitalha Please take a look!