Clear the composing range when selecting text. (#3635)
Clear the composing range when selecting text. (#3635)

This fixes a bug where editing the selected text on Android would delete
the wrong block of text.

BUG=https://github.com/flutter/flutter/issues/3567
tvolkert/flutter,cbracken/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,flutter/flutter,turnidge/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,tvolkert/flutter,tvolkert/flutter,aghassemi/flutter,cbracken/flutter,cbracken/flutter,turnidge/flutter,Hixie/flutter,cbracken/flutter,turnidge/flutter,aghassemi/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter,aghassemi/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,cbracken/flutter,Hixie/flutter,aghassemi/flutter,flutter/flutter,turnidge/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,turnidge/flutter,Hixie/flutter,cbracken/flutter,cbracken/flutter