Add more docs to framework.dart (#5944)
Add more docs to framework.dart (#5944)

There are still more to go, but this patch completes the widget section.
cbracken/flutter,cbracken/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,Hixie/flutter,turnidge/flutter,tvolkert/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,flutter/flutter,turnidge/flutter,tvolkert/flutter,tvolkert/flutter,turnidge/flutter,cbracken/flutter,turnidge/flutter,tvolkert/flutter,cbracken/flutter,flutter/flutter,tvolkert/flutter,tvolkert/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter,Hixie/flutter,turnidge/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,flutter/flutter,tvolkert/flutter