fix(ngModelOptions): initialize ngModelOptions in prelink

Input controls require `ngModel` which in turn brings in the `ngModelOptions`
but since ngModel does this initialization in the post link function, the
order in which the directives are run is relevant.

Directives are sorted by priority and name but `ngModel`, `input` and `textarea`
have the same priority. It just happens that `textarea` is alphabetically
sorted and so linked before `ngModel` (unlike `input`).

This is a problem since inputs expect `ngModelController.$options`
to exist at post-link time and for `textarea` this has not happened.

This is solved easily by moving the initialization of `ngModel` to the
pre-link function.

Closes #7281
Closes #7292
test(ngModelOptions): fix e2e test focussing
fix(ngModelOptions): enable overriding the default with a debounce of zero

Because of how the logic was set up, a value of `0` was assumed to be the
same as `undefined`, which meant that you couldn't override the default
debounce delay with a value of zero.

For example, the following assigned a debounce delay of 500ms to the `blur`
event.

```
ngModelOptions="{ updateOn: 'default blur', debounce: {'default': 500, 'blur':
0} }"
```

Closes #7205