Summary:
Previously <TextInput>'s onContentSizeChange event fires very rearly, usually just once after initial layout. This diff fixed that.
I also considered to a bunch of another things to get the native notification, but I found that overriding `onTextChanged` is the most reliable, easy and effitient way to implement this.
I tried/considered:
* onLayout (does not fire)
* OnPreDrawListener (fires to often)
* OnGlobalLayoutListener (does not fire)
* OnLayoutChangeListener (does not fire)
* isLayoutRequested (too hacky)
(I also fixed the <AutoExpandingTextInput> demo to illustrate the fix.)
And just heads up, we will remove `contentSize` info from `onChange` event very soon.
GH issue: https://github.com/facebook/react-native/issues/11692
Reviewed By: achen1
Differential Revision: D5132589
fbshipit-source-id: e7edbd8dc5ae891a6f4a87b51d9450b8c6ce4a1e