Add button to check which items use a feature layer

[StephenDickinson2]

It would be useful to be able to check a layer item for usage e.g. which web maps use a feature layer. This could be another button/link on the feature layer item details page.

I encounter this need when maintaining a portal and need to understand if a layer is in use and by what. I may be able to write some Python to do this but it would be nice to have this as a button in the interface that I could click on.

[RobertBorchert]

This is has been a high end request for many years for us.  At the least we would like to be able to see which Web Apps, Web Maps are being used by a Service.

The need for this has prompted us to change the way we make services.  We now only include a single Feature Dataset in a service.

But it would be very helpful to have this as a standard function.