This reverts commit 6e223c20.

1. 当存在tab为flutter vc的情况，切换到首页后，tab的flutter vc其还是live的状态，当回到首页点击进入某个flutter vc，然后回到首页之后，这个时候进行前后台切换，tab的flutter vc会进行active的回调，进行surfaceUpdated操作，但是这个时候engine.viewController并不是这个tab的flutter vc，会产生crash
2. 当退出某个flutter vc的时候之前可能是为了时许问题不影响别的已经设置好的engine.viewController所以没有进行detatch操作，这样会有可能导致最后退出的lutter vc不能及时释放

这种fix方法应该不是根本性的方案，但的确减少了线上相关crash日志

# Conflicts:
#	example/lib/simple_page_widgets.dart
#	lib/container/container_coordinator.dart

flutter 页面 连续push的时候，后面的flutter页面的voice over焦点会丢失

fix android platform demo, add custom method channel demo, add integration.md

Update Frequently Asked Question.md

fix typo.

merge code

Fix type cast error with `invokeMethod` method.

The root cause is that dart only returned `Map<dynamic, dynamic>` rather than specific generic type when `invokeMethod` was called. For more specific generic type user can use `cast<String, dynamic>` after the result was returned.

merge code

Update format according for flutter's analysis option

add custom dartEntrypoint

# Conflicts:
#	example/lib/simple_page_widgets.dart

# Conflicts:
#	android/src/main/java/com/idlefish/flutterboost/containers/FlutterActivityAndFragmentDelegate.java

merge code