Due to 339a165, it became impossible to filter nested properties of an object using the filterFilter.
A proposed solution to this was to enable the use of nested predicate objects. This change enables the
use of these nested predicate objects.
Example:
```html
<div ng-repeat="it in items | filter:{ address: { country: 'Canuckistan'}}"></div>
```
Or
```js
$filter('filter')(items, { address: { country: 'Canuckistan' } });
```
Closes#6215
Related to #6009
b4eed8ad94