For #21562 - Snap to next item when scrolling

This works by replacing the fling animation with snapping to the next item in
the scroll direction.

app/src/main/java/org/mozilla/fenix/compose/LazyListEagerFlingBehavior.kt

@@ -0,0 +1,47 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.fenix.compose
+
+import androidx.compose.foundation.gestures.FlingBehavior
+import androidx.compose.foundation.gestures.ScrollScope
+import androidx.compose.foundation.lazy.LazyListState
+import androidx.compose.foundation.lazy.LazyRow
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.rememberCoroutineScope
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.launch
+
+/**
+ * [FlingBehavior] for a [LazyRow] that will automatically scroll the list in the fling direction
+ * to fully show the next item.
+ */
+@Composable
+fun EagerFlingBehavior(
+    lazyRowState: LazyListState
+): FlingBehavior {
+    val scope = rememberCoroutineScope()
+
+    return LazyListEagerFlingBehavior(lazyRowState, scope)
+}
+
+private class LazyListEagerFlingBehavior(
+    private val lazyRowState: LazyListState,
+    private val scope: CoroutineScope
+) : FlingBehavior {
+    override suspend fun ScrollScope.performFling(initialVelocity: Float): Float {
+        val firstItemIndex = lazyRowState.firstVisibleItemIndex
+
+        val itemIndexToScrollTo = when (initialVelocity <= 0) {
+            true -> firstItemIndex
+            false -> firstItemIndex + 1
+        }
+
+        scope.launch {
+            lazyRowState.animateScrollToItem(itemIndexToScrollTo)
+        }
+
+        return 0f // we've consumed the entire fling
+    }
+}

app/src/main/java/org/mozilla/fenix/home/sessioncontrol/viewholders/pocket/PocketStoriesComposables.kt

@@ -18,6 +18,7 @@ import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.lazy.LazyRow
 import androidx.compose.foundation.lazy.itemsIndexed
+import androidx.compose.foundation.lazy.rememberLazyListState
 import androidx.compose.material.Icon
 import androidx.compose.material.Text
 import androidx.compose.runtime.Composable
@@ -37,6 +38,7 @@ import mozilla.components.service.pocket.PocketRecommendedStory
 import mozilla.components.ui.colors.PhotonColors
 import org.mozilla.fenix.R
 import org.mozilla.fenix.compose.ClickableSubstringLink
+import org.mozilla.fenix.compose.EagerFlingBehavior
 import org.mozilla.fenix.compose.FakeClient
 import org.mozilla.fenix.compose.ListItemTabLarge
 import org.mozilla.fenix.compose.ListItemTabLargePlaceholder
@@ -96,8 +98,10 @@ fun PocketStories(
 ) {
     // Show stories in a 3 by 3 grid
     val gridLength = 3
+    val listState = rememberLazyListState()
+    val flingBehavior = EagerFlingBehavior(lazyRowState = listState)
 
-    LazyRow {
+    LazyRow(state = listState, flingBehavior = flingBehavior) {
         itemsIndexed(stories.chunked(gridLength)) { rowIndex, columnItems ->
             Column(Modifier.padding(end = if (rowIndex < gridLength - 1) 8.dp else 0.dp)) {
                 for (index in 0 until gridLength) {