Start the filter.
- iOS 9.0+
- macOS 10.15+Beta
- UIKit for Mac 13.0+Beta
A block that must be executed when the filter is running and is ready to filter network content.
This method is called by the system to start the filter.
NEFilter subclasses must override this method.
When this method is called, the Filter Provider should perform any steps necessary to initialize the filter and then execute the