docs(CHANGELOG.md): add breaking change from 5f3f25a1

5f3f25a1 included a breaking change which was not documented, which is that the return value of directive
constructors is ignored. The reason they are ignored is to ensure that the correct object is bound to when
binding properties to the controller. It may be possible to come up with a better solution which informs
the developer that what they are doing is wrong, rather than just breaking instead.

Closes #8876
Closes #8882