feat(dateFilter): add `utc` argument to format in UTC.

If a truthy value is passed in as the third argument to dateFilter,
it will format in UTC rather than local time.

Closes #6546
This block isn't quite right. If UTC dates are needed, you need to use [`Date.UTC`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/UTC) to initialize the Date object, like: `new Date( Date.UTC(y, m, d) )`. Otherwise, the resulting date may have the wrong date (due to timezone conversion).