feat: expose isAtEnd shared value from KeyboardChatScrollView

[jkinggg]

📜 Description

This PR adds an optional isAtEnd?: SharedValue<boolean> prop to KeyboardChatScrollView.

When provided, the component updates that shared value on the UI thread using the same internal scroll metrics and isScrollAtEnd(...) logic already used by keyboardLiftBehavior="whenAtEnd".

The goal is to let chat-style apps build jump-to-latest / scroll-to-bottom affordances without reimplementing the component's internal "at end" logic in app code.

💡 Motivation and Context

This change is intended to solve a common gap in chat UIs:

• the component already knows whether the user is effectively at the end
• apps often need that same signal for follow-mode and jump-to-latest UI
• today, consumers must guess based on external scroll heuristics

That duplication is brittle because app-side heuristics can diverge from the component's own keyboard-aware behavior.

This PR keeps the API small by exposing the semantic state (isAtEnd) instead of lower-level raw scroll metrics.

Related issue: #1430

📢 Changelog

JS

• add optional isAtEnd?: SharedValue<boolean> prop to KeyboardChatScrollView
• update isAtEnd on the UI thread using existing isScrollAtEnd(...) logic
• add TypeScript declarations for the new prop

iOS

• no native changes

Android

• no native changes

🤔 How Has This Been Tested?

Validated in the fork clone with:

• yarn typescript
• yarn lint src/components/KeyboardChatScrollView/index.tsx src/components/KeyboardChatScrollView/types.ts

Not yet completed before opening this draft PR:

• yarn test
• manual verification in the example app on iOS
• manual verification in the example app on Android

📸 Screenshots (if appropriate):

No screenshots yet. This draft PR is mainly to support API discussion from #1430.

📝 Checklist

• CI successfully passed
• I added new mocks and corresponding unit-tests if library API was changed

[kirillzyusko]

Hey @jkinggg

Is it final PR? Can we move it to "ready for review" stage?

[jkinggg]

Hey @kirillzyusko this is ready

[github-actions]

📊 Package size report

Current size	Target Size	Difference
313911 bytes	312781 bytes	1130 bytes 📈