feat(ngAria): add an ngAria module to make a11y easier

I made some significant refactors to #8342, notably:

* DRYing up the implementation
* unDRYing up the specs so that the assertions/failures are more specific
* Naming watch functions to make debugging easier
We could. Actually for most of these cases here and it would be even faster.
The idea was that we don't want to add more code to Angular core for people that don't need aria support.