fix(android): support multiple pager instances (#242)

Author: alpha0010

android/src/main/java/com/reactnativecommunity/viewpager/FragmentAdapter.java

@@ -9,6 +9,8 @@
 import com.reactnative.community.viewpager2.adapter.FragmentStateAdapter;
 
 import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 
 public class FragmentAdapter extends FragmentStateAdapter {
 
@@ -59,6 +61,10 @@ public void removeAll() {
         notifyDataSetChanged();
     }
 
+    public List<Integer> getChildrenViewIDs() {
+        return Collections.unmodifiableList(childrenViewIDs);
+    }
+
     public int getChildViewIDAt(int index) {
         return childrenViewIDs.get(index);
     }

android/src/main/java/com/reactnativecommunity/viewpager/ReactViewPagerManager.java

@@ -127,7 +127,9 @@ public void removeView(ViewPager2 parent, View view) {
 
     public void removeAllViews(ViewPager2 parent) {
         FragmentAdapter adapter = ((FragmentAdapter) parent.getAdapter());
-        reactChildrenViews.clear();
+        for (int childID : adapter.getChildrenViewIDs()) {
+            reactChildrenViews.remove(childID);
+        }
         adapter.removeAll();
         parent.setAdapter(null);
     }