Merge options into popped screen correctly

Options were merged after screen was popped from the backing stack data structure.
This meant that options were not resolved correctly for it as it was already detached from the stack.
This was especially noticeable when declaring a custom animation is mergeOptions passed to Navigation.pop().

Fixes #3869 and closes #4138

lib/android/app/src/main/java/com/reactnativenavigation/viewcontrollers/stack/StackController.java

             return;
         }
 
+        peek().mergeOptions(mergeOptions);
+        Options disappearingOptions = resolveCurrentOptions();
+
         final ViewController disappearing = stack.pop();
         final ViewController appearing = stack.peek();
-        disappearing.mergeOptions(mergeOptions);
+
         disappearing.onViewWillDisappear();
         appearing.onViewWillAppear();
+
         Options resolvedOptions = resolveCurrentOptions();
         ViewGroup appearingView = appearing.getView();
         if (appearingView.getLayoutParams() == null) {
             getView().addView(appearingView, 0);
         }
         presenter.onChildWillAppear(appearing.options, disappearing.options);
-        if (disappearing.options.animations.pop.enabled.isTrueOrUndefined()) {
-            animator.pop(disappearing.getView(), resolvedOptions.animations.pop, () -> finishPopping(disappearing, listener));
+        if (disappearingOptions.animations.pop.enabled.isTrueOrUndefined()) {
+            animator.pop(disappearing.getView(), disappearingOptions.animations.pop, () -> finishPopping(disappearing, listener));
         } else {
             finishPopping(disappearing, listener);
         }

lib/android/app/src/test/java/com/reactnativenavigation/viewcontrollers/stack/StackControllerTest.java

 package com.reactnativenavigation.viewcontrollers.stack;
 
+import android.animation.Animator;
 import android.app.Activity;
 import android.content.Context;
 import android.view.View;
 import com.reactnativenavigation.mocks.TitleBarReactViewCreatorMock;
 import com.reactnativenavigation.mocks.TopBarBackgroundViewCreatorMock;
 import com.reactnativenavigation.mocks.TopBarButtonCreatorMock;
+import com.reactnativenavigation.parse.AnimationOptions;
 import com.reactnativenavigation.parse.NestedAnimationsOptions;
 import com.reactnativenavigation.parse.Options;
 import com.reactnativenavigation.parse.params.Bool;
 import com.reactnativenavigation.views.topbar.TopBar;
 
 import org.assertj.core.api.iterable.Extractor;
+import org.json.JSONException;
 import org.json.JSONObject;
 import org.junit.Test;
 import org.mockito.ArgumentCaptor;
     }
 
     @Test
-    public void popDoesNothingWhenZeroOrOneChild() {
+    public void pop_doesNothingWhenZeroOrOneChild() {
         assertThat(uut.isEmpty()).isTrue();
         uut.pop(Options.EMPTY, new CommandListenerAdapter());
         assertThat(uut.isEmpty()).isTrue();
         assertContainsOnlyId(child1.getId());
     }
 
+    @SuppressWarnings("MagicNumber")
+    @Test
+    public void pop_animationOptionsAreMergedCorrectlyToDisappearingChild() throws JSONException {
+        disablePushAnimation(child1, child2);
+
+        uut.push(child1, new CommandListenerAdapter());
+        uut.push(child2, new CommandListenerAdapter());
+
+        Options mergeOptions = new Options();
+        JSONObject content = new JSONObject();
+        JSONObject x = new JSONObject();
+        x.put("duration", 300);
+        x.put("from", 0);
+        x.put("to", 1000);
+        content.put("x", x);
+        mergeOptions.animations.pop.content = AnimationOptions.parse(content);
+
+        uut.pop(mergeOptions, new CommandListenerAdapter());
+        ArgumentCaptor<NestedAnimationsOptions> captor = ArgumentCaptor.forClass(NestedAnimationsOptions.class);
+        verify(animator, times(1)).pop(any(), captor.capture(), any());
+        Animator animator = captor.getValue().content
+                .getAnimation(mock(View.class))
+                .getChildAnimations()
+                .get(0);
+        assertThat(animator.getDuration()).isEqualTo(300);
+    }
+
     @Test
     public void canPopWhenSizeIsMoreThanOne() {
         assertThat(uut.isEmpty()).isTrue();