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
The value of `aria-checked` should change from `true` to `false` as the element is checked, it is not a boolean attribute.