poc(expo-ui): drive native toolbar from LazyColumn

[AmatoGiulio]

Explores Expo UI LazyColumn as a real Compose-owned scroll source for react-native-scroll-interop.

POC scope:

• keep Expo UI LazyColumn as the scroll owner
• bridge Compose nested scroll into the Android View nested-scroll chain with rememberNestedScrollInteropConnection()
• accept the hosting ComposeView as a generic nested-scroll transaction source without adding a compile-time Compose dependency to the core
• drive the existing Material 3 FloatingToolbar from that transaction
• intentionally leave TopAppBar scroll-away geometry out of scope for this first proof, because its current adapter uses RN-specific scroll-away padding

The example carries a temporary SDK 57 patch script that registers a nestedScrollInterop Expo UI modifier. The intended upstream Expo API is a generic modifier, independent of this library.

Local validation target:

1. install examples/expo dependencies (refreshes its lockfile with direct @expo/ui@57.0.12)
2. prebuild/run Android so the temporary Expo UI Kotlin patch is compiled
3. open Expo UI LazyColumn POC
4. verify touch scroll and fling both hide/restore the native FloatingToolbar without moving the source outside Compose

This is deliberately a draft POC and should not merge as-is; the node_modules patch is evidence for the upstream Expo change, not a shipping integration.

[AmatoGiulio]

Upstream Expo UI proposal

The POC needs only a generic Expo UI modifier; no react-native-scroll-interop knowledge belongs upstream.

Android

In packages/expo-ui/android/src/main/java/expo/modules/ui/ModifierRegistry.kt:

import androidx.compose.ui.input.nestedscroll.nestedScroll
import androidx.compose.ui.platform.rememberNestedScrollInteropConnection

and in registerBuiltInModifiers():

register("nestedScrollInterop") { _, _, _, _ ->
  Modifier.nestedScroll(rememberNestedScrollInteropConnection())
}

JS API

In packages/expo-ui/src/jetpack-compose/modifiers/index.ts:

/**
 * Connects a Compose nested-scroll chain to a cooperating Android View
 * `NestedScrollingParent3` ancestor.
 *
 * This wraps Compose's `rememberNestedScrollInteropConnection()` and is useful
 * when an Expo UI scrollable is hosted inside an Android View hierarchy that
 * participates in AndroidX nested scrolling.
 */
export const nestedScrollInterop = () => createModifier('nestedScrollInterop');

Usage:

<LazyColumn modifiers={[fillMaxSize(), nestedScrollInterop()]}>
  {...}
</LazyColumn>

This is intentionally a generic Compose/View interop primitive. The local POC's node_modules patch mirrors this proposed upstream implementation.