Allow overriding the time interval and full time extent in the TimeSlider toolkit in Qt

[Gela]

I would like to be able to use a time enabled feature layer that is missing the time interval value, but given that there is no way to manually override that, we cannot utilize that service.

As per Ting 's suggestion, this appears to be possible in the iOS toolkit.

there is an initializer for the iOS TimeSlider to instantiate with a “full time extent”: https://github.com/Esri/arcgis-runtime-toolkit-ios/tree/master/Documentation/TimeSlider#usage

public func initializeTimeSteps(timeStepCount: Int, fullExtent: AGSTimeExtent, completion: @escaping (Error?)->Void)

In iOS it is also possible to set the full time extent using the property:

timeSlider.fullExtent = AGSTimeExtent(startTime: startTime, endTime: endTime)