Add unveilIn and veilOut animations to default iOS transition specs (#2655)

Fixes https://youtrack.jetbrains.com/issue/CMP-9003

## Release Notes
### Features - Navigation
- Add `unveilIn` and `veilOut` animations to default iOS transition
specs in Navigation3

Author: terrakok

navigation3/navigation3-ui/src/iosMain/kotlin/androidx/navigation3/ui/NavDisplay.ios.kt

@@ -18,20 +18,24 @@ package androidx.navigation3.ui
 
 import androidx.compose.animation.AnimatedContentTransitionScope
 import androidx.compose.animation.ContentTransform
+import androidx.compose.animation.ExperimentalAnimationApi
 import androidx.compose.animation.core.CubicBezierEasing
 import androidx.compose.animation.core.LinearEasing
 import androidx.compose.animation.core.spring
 import androidx.compose.animation.core.tween
 import androidx.compose.animation.fadeIn
 import androidx.compose.animation.fadeOut
 import androidx.compose.animation.scaleOut
+import androidx.compose.animation.unveilIn
+import androidx.compose.animation.veilOut
 import androidx.navigation3.scene.Scene
 import androidx.navigationevent.NavigationEvent.Companion.EDGE_LEFT
 import androidx.navigationevent.NavigationEvent.SwipeEdge
 
 private const val DEFAULT_TRANSITION_DURATION_MILLISECOND = 500
 private val IosTransitionEasing = CubicBezierEasing(0.2833f, 0.99f, 0.31833f, 0.99f)
 
+@OptIn(ExperimentalAnimationApi::class)
 public actual fun <T : Any> defaultTransitionSpec():
     AnimatedContentTransitionScope<Scene<T>>.() -> ContentTransform = {
     ContentTransform(
@@ -43,17 +47,22 @@ public actual fun <T : Any> defaultTransitionSpec():
             towards = AnimatedContentTransitionScope.SlideDirection.Left,
             targetOffset = { it / 4 },
             animationSpec = tween(DEFAULT_TRANSITION_DURATION_MILLISECOND, easing = IosTransitionEasing),
+        ) + veilOut(
+            animationSpec = tween(DEFAULT_TRANSITION_DURATION_MILLISECOND, easing = IosTransitionEasing),
         ),
     )
 }
 
+@OptIn(ExperimentalAnimationApi::class)
 public actual fun <T : Any> defaultPopTransitionSpec():
     AnimatedContentTransitionScope<Scene<T>>.() -> ContentTransform = {
     ContentTransform(
         slideIntoContainer(
             towards = AnimatedContentTransitionScope.SlideDirection.Right,
             initialOffset = { it / 4 },
             animationSpec = tween(DEFAULT_TRANSITION_DURATION_MILLISECOND, easing = IosTransitionEasing),
+        ) + unveilIn(
+            animationSpec = tween(DEFAULT_TRANSITION_DURATION_MILLISECOND, easing = IosTransitionEasing)
         ),
         slideOutOfContainer(
             towards = AnimatedContentTransitionScope.SlideDirection.Right,
@@ -62,6 +71,7 @@ public actual fun <T : Any> defaultPopTransitionSpec():
     )
 }
 
+@OptIn(ExperimentalAnimationApi::class)
 public actual fun <T : Any> defaultPredictivePopTransitionSpec():
     AnimatedContentTransitionScope<Scene<T>>.(@SwipeEdge Int) -> ContentTransform = { edge ->
     val towards = if (edge == EDGE_LEFT) {
@@ -74,6 +84,8 @@ public actual fun <T : Any> defaultPredictivePopTransitionSpec():
             towards = towards,
             initialOffset = { it / 4 },
             animationSpec = tween(DEFAULT_TRANSITION_DURATION_MILLISECOND, easing = LinearEasing),
+        ) + unveilIn(
+            animationSpec = tween(DEFAULT_TRANSITION_DURATION_MILLISECOND, easing = LinearEasing),
         ),
         slideOutOfContainer(
             towards = towards,