feat(ngMock): allow the use of a predicate to match data

[jnizet]

When using $httpBackend, the data in definitions and expectations can only
be defined as a string (which must be matched exactly) or as a regexp.
Both are not very practical when it comes to matching JSON objects. This
commits adds the possibility to pass a predicate function, which should
return a truthy value if the data matches with the expectation and a falsy
value if it doesn't.

[mary-poppins]

Thanks for the PR!

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Thanks again for your help!

[jnizet]

My real name is Jean-Baptiste Nizet. I just signed the CLA.
I don't see where my commit message doesn't respect the commit message format, sorry.

[petebacondarwin]

Hi @jnizet - Thanks for this PR. It is actually a duplicate of #2981. So closing and let's see if we can get that one merged.