feat(filterFilter): support filterFilter for object literal collection

Request Type: feature

How to reproduce: Feed an object literal into an ngRepeat to loop over its properties with a filter in use, as shown here: http://plnkr.co/edit/mMvAgQgILcBVkbT2q4z4?p=preview

Component(s): misc core

Impact: small

Complexity: small

This issue is related to:

Detailed Description:

I switched the primary filterFilter iteration method to one that supports both array and object literal collections and added tests for the object version.

Other Comments:

filterFilter was previously only available to array/array-like collections,
but ngRepeat supports iterating over object literals. This PR enables
filtering functionality over object literal properties.

Fixes #6490
It is safe to use `Object.keys` since it is available in all browsers supported in 1.3.x.