fix: trigger onViewableItemsChanged when calling MasonryFlashList's recomputeViewableItems after data changed

[zyestin]

I am glad to see that @Paduado has added the recomputeViewableItems method to solve the problem that the onViewableItemsChanged will not be called after the FlashList's data is updated.
But the MasonryFlashList I used in my project did not enjoy this benefit.
So I changed the MasonryFlashList source code to achieve the same effect as FlashList.

Reviewers’ hat-rack 🎩

• Validate that calling the recomputeViewableItems method triggers the onViewableItemsChanged callback.

Screenshots or videos (if needed)

Checklist

• I have added a changelog entry following the Keep a Changelog guidelines.

[zyestin]

I have signed the CLA!

[zyestin]

Hi, @naqvitalha. Can you review my commit, which is very relevant to the last PR #1296 you were involved.

[naqvitalha]

Hi! 👋 Thank you for your contribution to FlashList!

We're now focusing exclusively on FlashList v2 and React Native's New Architecture. As part of this transition, we're closing older pull requests to better focus our review efforts on v2-compatible changes.

If your changes are still relevant:

• Please verify they work with FlashList v2
• Rebase against the latest main branch
• Open a new PR with v2 compatibility in mind
• We'll be happy to review it!

Resources:

• Contributing Guide
• FlashList v2 Documentation

We truly appreciate your effort and contribution. Thank you for helping make FlashList better! 🙏