Document that State#build(BuildContext context) is always the same as State#context (#4116)
Document that State#build(BuildContext context) is always the same as State#context (#4116)

Fixes #4114
tvolkert/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,turnidge/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,Hixie/flutter,aghassemi/flutter,flutter/flutter,cbracken/flutter,Hixie/flutter,Hixie/flutter,turnidge/flutter,flutter/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,Hixie/flutter,aghassemi/flutter,Hixie/flutter,tvolkert/flutter,cbracken/flutter,cbracken/flutter,turnidge/flutter,cbracken/flutter,tvolkert/flutter,tvolkert/flutter,cbracken/flutter,tvolkert/flutter,aghassemi/flutter,cbracken/flutter,tvolkert/flutter,turnidge/flutter,aghassemi/flutter,cbracken/flutter,cbracken/flutter,turnidge/flutter,flutter/flutter,flutter/flutter,flutter/flutter,Hixie/flutter