- Full support for content projection in downgraded Angular 2
components. In particular, this enables multi-slot projection and
other features on <ng-content>.
- Correctly wire up hierarchical injectors for downgraded Angular 2
components: downgraded components inherit the injector of the first
other downgraded Angular 2 component they find up the DOM tree.
Closes#6629, #7727, #8729, #9643, #9649, #12675
