feat(filterFilter): allow overwriting the special `$` property name

Previously, the special property name that would match against any
property was hard-coded to `$`.
With this commit, the user can specify an arbitrary property name,
by passing a 4th argument to `filterFilter()`. E.g.:

```js
var items = [{foo: 'bar'}, {baz: 'qux'}];
var expr  =  {'%': 'bar'};

console.log(filterFilter(items, expr, null, '%'));   // [{foo: 'bar'}]
```

Fixes #13313
PR (#13356)